I care for my mother (95) in my home. She is scratching and scratching. I administer itch creams, like benadryl or cortisone.

Renal function?

Some medicines can cause this also,, take a look at what she is on and let her Dr know

1.  What's the normal temperature in the living environment?

2.   Is there a humidifier that can be refilled regularly to humidify the air?

3.   Is there a humidifier on the furnace?

4.   Is there a hygrometer that measures the moisture in the air?  If so, what's the normal reading?  

5.   Are her clothes of natural fibers (if that's even possible these days) or synthetics?

I raise these issues in part b/c I don't turn to meds as a first option; herbals are my go-to choice, and I buy them only from trusted buyers with whom I've been dealing for about 20 years.  

5.   Have you ever tried natural remedies?   My legs have been itching since the frigid weather set in and the heat is on longer and higher.  Last night I put some herbal lotion containing Rosemary, mint, lavender and a variety of natural substances.  It works better than anything except Shea butter.   I've been using it for years.  

Notwithstanding these suggestions, I think a trip to a dermatologist should be considered, especially if this is a long standing issue.  There might be something else going on with your mom's skin.

sometimes it can be the detergent used for clothing ,linens,etc. you can try a "free and clear" detergent or a baby/ infant soap.
stress can trìgger rashes and hives so pay attention if this is possible in your situation. ive also used antifungal powders (can be athletes foot powders) and that helped dramatically with patients yeast skin rashes good luck🤞

Please be cautious of Benadryl or products labeled as "PM" (any thing with diphenhydramine)
This product can make you sleepy and anyone with a balance problem should be cautious.
I also realized after I took it one night (I had been giving it to my Husband for his allergies) I woke up with what I called a "foggy brain" I realized that it might be having the same effect on my Husband and the last thing someone with dementia needs is a "foggy brain" so I stopped giving it to him.

Have you had her skin issues assessed by a dermatologist?

Too MUCH bathing can cause problems. Too little can also. Using 'dry shampoos' and 'no rinse' bathing products are fine for a little while, but are not meant for long term use. They are both drying.

Cortisone can thin out the skin and make the itching worse. Go easy on that.

I have found that Amlactin has worked pretty well for dryness on my elbow and gross scaly feet (also wearing shoes would help with that :)

For showers, I use a body wash called Lume and it is not drying at all. Many itches come from dry skin--if you can attack the source, you may not have to use bendadryl. I have heard that benadryl is not really good for the elderly, but at 95, just keeping mom comfortable would be all I'd be concerned about.

Do you have her use an electric throw or blanket? That can cause problems like this.