My 90 year old mom has recently been eating more than usual. She's forgetting she ate minutes earlier, what she ate, and which meal she ate. She does eat well so it surprises me when she says she's hungry right after a good meal. This is something new. 6-8 months ago I would have to remind her to eat! I would have to get her to eat so she could take her meds. She does have Alzheimer's. Im not sure what stage she's in or when dementia end/begins and Alzheimer's takes over. No change in meds.
The not remembering she just ate is extremely common. My mother can say "I'm waiting for them to take my lunch order" when the dirty dishes from her lunch are still sitting in front of her! If we say, "Well, Mom, I think you've had your lunch. Should we go for a walk now, and if you are hungry when we get back we'll find a snack for you?" she is generally OK with that.
How does your mother react when you suggest she wait a little while for a snack? If she accepts that and can be distracted, no problem. If she insists she wants to eat right now and why are you being so mean, then perhaps keeping lots of snacks on hand would be useful. Can she eat nuts? A bowl of in-the-shell peanuts would give her something to do for a while, as well as something to eat. A Popsicle would also last a little while and contribute toward hydration. A handful of cherries, if she can be relied on to spit out the pits.
This won't last forever, either. As long as she isn't gaining a lot of weight or messing up a diabetic blood sugar problem, I'd just go with the flow.
Alzheimer's is just a name for one kind of dementia. There are about 50 kinds total. But whatever kind she has and whatever stage she is in, you have to deal with the symptoms she is exhibiting now.
One day at a time!