Is anyone aware of controlling a diet as a way of improving memory, controlling confusion and/or anger?

Fisherman, oh how we wish changing one's diet or adding certain vitamins would help with dementia, but it doesn't.

I think what is happening with your wife is that she is showing signs of "sundowning" which makes the symptoms show stronger starting in later afternoon and through the night time [it can also start earlier in the afternoon].

If your wife is tired, have the doctor check her vitamin B levels.  If low, adding more vitamin B could make her less tired.   Or it may not.   Or she might be active around the clock.   One never knows at this point in the time how a person will react.

Don't forget adequate hydration...so many elderly are dehydrated and that adds to confusion and even balance issues.

My mom suffers end stage Alzheimer's and what helps me a LOT is daily exercise. It took over a year but I got her to walk close to a half mile (about 3/4th of a half mile-most of it) -- when she first started she could not even do a half block without getting extremely short of breath and wheezing. After a considerable time she is no longer short of breath and no longer wheezes. Walking does a LOT to control behavior. I do it every morning. If I can't walk her outside due to rain or other bad weather, I take her to the mall. I do this seven days a week. I also give her a cup of cocoa daily. Usually during lunch I will make a cup of cocoa and put two tablespoons in it (heaping) with soy milk (we don't do dairy products). After about two weeks you will notice a difference for the better. Walking is the most essential medicine--I consider it like a daily routine medication -- and if she gets confused or out of control in the afternoon we go walking again and it straightens her right out. I also keep her awake during the day. Along with her cocoa in the afternoon make a very strong green tea (concentrated) and mix it in with the cocoa drink. It really does help. But if I didn't walk her she would be either bedridden or dead by now. It also helps prevent falls. They still happen but not nearly as much as they used to. 
When I walk my mom she uses a WALKER. There is no way she can walk nearly a half mile without her walker--and remember it took over a year to get her to walk that far. It took one year to get her to walk a quarter of a mile. She can go a little further now.  Also keeping her awake during the day she generally sleeps all night. I use NO narcotics and NO psychotropic DRUGS. Psychotropic medications increase risk for falling and only mask symptoms.   I say keep them moving.   If I don't exercise her she can be most difficult. Exercise is the key. but gradually introduce it and gradually increase tolerance. It takes time. With exercise she's a lot better and improved her quality of life..and mine.

I'd discuss your wife's dementia symptoms with her doctor. Is she still able to have input into her treatment? I'm not a doctor or expert, but, to my knowledge, unfortunately, nutrition and supplements have not been proven to have any effect on brain damage, which is what occurs with dementia. While a healthy diet is great and certainly benefits a person's overall health, I'd ask the doctor if any kind of restrictive diet or supplements is advised for her dementia.

To me, my loved one's quality of life is more important than depriving her of her favorite treats. I make sure she gets them on a regular basis. Her pleasure and enjoyment is very important to me than a strict diet that is not going to prolong her life. Dementia is a terminal illness, so, for me, making every day happy for her is my goal.

If your wife seems to have mental distress that continues, ask your doctor if medication would be helpful or if there are things that could do that might make her feel better, like gentle music. I've read that playing those CD's of relaxing music, sounds of nature, waterfalls, birds, can help calm a dementia patient.

I would be wary of those who offer promises to help or reverse dementia with diet or supplements.  I think that desperation and grief can make us place our faith in any number of cures, treatments.  If in doubt, discuss it with a Neurologist, psychiatrist of even her primary doctor.  

Being tired and hungry doesn't exactly improve my temper or willingness to concentrate, either. I'm not quite sure what, beyond the obvious, you're hoping to discover?

If your wife is beginning to show clear signs of dementia, it's a good time to think about structuring her environment and her day anyway. She'll feel more secure if things run to a reliable timetable, plus you'll be able to see where the gaps between mealtimes are too long and maybe shift things around a bit.

Exercise is good for everyone, I agree; ideally out of doors, in good daylight; and my mother's mental health nurse also recommended a 1-2 hour nap after lunch.

And what the heck is a 'sugar supplement'??? No. Try a sandwich, or a couple of crackers with some cream cheese. Except for diabetics going hypo, it is hard to think of *anyone* who needs more sugar in their diet.

I'm afraid there is no magic diet. If only there were!

One thing you can try is moving the evening a little earlier. Or perhaps have a snack mid-afternoon. Crackers and cheese. Apple wedges and peanut butter. A small dish of ice cream. Not a whole meal, just a little pick-me-up. Some people need to eat more often to keep their blood sugar levels from slumping. This may have nothing to do with your wife's problems, but it is an easy thing to try.

(I worked with a guy once who got crabby if his lunch was delayed. He kept a box of snickers in his desk drawer and ate one if it looked like lunch might be late. )

Fisherman,
You are on the right track and Cetude, a few others are right there with you. Exercise, Hydration, and Nutrition are Keys to Life!
At our small ALF home in Pembroke Pines, FL, we have seen amazing results with Walking, being Outside where the Sunshine is on our skin, and Yes, Daily Routine. I, myself as a caregiver and a person, have seen and felt amazing improvement in my own health and focus with this program.

We use only healthy foods, whole wheat bread, brown rice, whole wheat or veggie/bean pasta with extra protein, quinoa, spelt berries, steel cut oats, not the mushy ones. Lots of fruits and vegetables, and plenty of pure Water, by reverse osmosis, that filters out the chlorine, fluoride and other chemicals, without causing the huge waste of plastic bottles for the environment.
We use Coconut Oil, Coconut Milk and Coconut Water. With enough fiber and Hydration, people eliminate better, and think clearer. The exercise is also Key and that they get Outside Daily to see the Sun, to be Connected again to the timeless rhythm of life and this helps hugely in the prevention of sundowning.
Change your light bulbs in the home (yeah, a hundred or two but Worth it!) to Daylight color spectrum, so that even when it's not friendly out to that walk, she gets Daylight Every day. Don't let her sleep in the daytime, keep her busy. Get her up Early with the Sun, the Natural way, and Limit Screen Time. That Blue light emitted Causes Insomnia, the last thing you need.
Cetude is right, Daily Routine, Same time and they will Ask to go for a walk. It really is that easy, when you get it going. People with memory loss feel so much Safer if they Know what to expect, Daily.

The symptoms you describe prior to the evening meal is known as "Sundowners". As the sun begins to set the body starts a chemical change in the brain of a person with dementia. The brain loves rich omega 3s found in eggs, fish, salmon, etc. However if you have been following the centenarians lately who are well over 100+, they eat bacon, eggs, cookies, and have the blessings of their doctors. Dementia is a terminal illness, so feed her whatever she likes.

You will learn that it is easier to change your routine than it is to change her.
You will need to adapt.
Make your larger meal in the afternoon. (healthier anyway according to my Grandma..Eat breakfast like a King, Lunch like a Prince and dinner like a Pauper)
This will eventually change so her larger more substantial meal will be in the morning.
She gets exhausted trying to keep things straight in her mind. Who she is, who you are, where she is, do underpants go on first or the long pants, do you put shoes on first or pants, where the bathroom is, what to do when she gets there. This is making her mind work even harder. Maybe even how to walk, how to open a door.
Doing all this takes a lot of energy so by the mid afternoon early evening she is done!.
The restlessness in the evening commonly called "Sundowning" can be anything from pure frustration, wandering , anger or any OCD becomes more pronounced.
Keep the lights on as much as possible. Switch lights to LED they seem to be brighter and more true to a sunlight. (They also use less energy and if you have to keep lights on that's a good thing)
It can be anything from shadows to exhaustion that causes more problems. Eye sight is not great at this stage in our lives and with dementia we have no idea what the shadows do to trick the eye or mind.
She will sleep more during the day and longer in the morning and maybe even want to go to bed earlier. This is normal and it is a way for the body to try to rest and prepare for the next day and try to repair itself. And with any dementia repair is impossible but the body keeps trying.
Bottom line when it comes to adapting to a new routine you must be the one that adapts. It makes it much easier and less frustrating for all.

That is a good point Ferris. I don't know of anyone who is over the age of 80 that has lived on a restrictive diet. They all eat a full diet of fats, carbs, protein, including bacon, cakes, ice cream, etc.