Does she have any relatives you can talk to? 

Sounds like early onset dementia but I'm no expert.  My neighbour asks me every 10 minutes how old I am. Doubt if there's anything you can do except be there for her.  Does she have family who may want to get a diagnosis?

9.52 - sorry your response wasn't there when I answered.  I would just leave it so long as she is safe.

Suggest she sees her GP for a check up.

If she refuses,  write to them explaining your concerns about her.

They won't discuss her with you but should invite her to a 'routine wellness check'.

Of course if she deteriorates and you are worried about her safety, contact adult social services.

Nobody would know that you wrote to her GP.

Otherwise there is absolutely nothing you can do

Oh! No, it could be nothing, it could be symptoms of many things. 

Have you asked her why she rang you in the middle of the night?

It's not unusual for seemingly minor worries to get out of proportion when you live alone, with a lot of time on your hands.

Bearing in mind that it gets light quite early in the morning at this time of year, she might just have woken up, seen the daylight and rung you up. Some years ago I was talking to a lady in her 40s that I worked with. She told be she'd  embarrassed herself; she'd woken up, had her bath and got ready for work and then realised it was only 3am. It can happen to anybody.

barry is spot on....if the family won't take this seriously, contact your local surgery and, failing this and concerns about her overall safety then contact adult social services.

The one thing it isn't is early onset dementia - that applies to people who get dementia much younger.

It could be early symptoms of dementia, though. There are drugs that can slow the progress of dementia and the sooner they are started the better. Sadly, there is a very long process between initial assessy and diagnosis. I'm hearing of it taking over 14 months in many cases.

Hopefully it's not that.