dementia

[user1486156729]

I'm late sixties, and my dear friend is a bit younger than I am. Her father and his brother had dementia.
Looks like (to me) she's in the early stage of this - doesn't remember entire conversations we've had.
When she says she doesn't remember, I just say, oh ok, as I don't want to distress her.
I don't know what to do, or if there's anything I could do.
She has no family to help.
I'll help for as long as I can.

Speak to her about it. Is she missing bits from sequences (like forgets to put the teabag in the cup) or just struggling to hold a conversation?

Try and get her to her gp first of all

I agree, encouraging her to speak to her GP is a good step. Could you frame it in an "I'm worried about you, you don't seem yourself lately, for example x y z, is there anything worrying you?"
It could be there's another health issue going on, or it could be that she is worried about it herself and is nervous about going to her GP because she doesn't want to be diagnosed. There's some really good info on the Alzheimer's Society website which might be worth a read.
Your friend is very lucky to have such a caring friend to support her.

I would definitely speak to her. Is she on a lot of medication? I ask because pharmaceutical-related dementia is very common, so she many need to discuss this with her doctor.