My DM was diagnosed with Alzheimer's dementia nearly 3 years ago. She has been living independently in her own flat (which has an emergency call system), but recently her mobility has taken quite a hit and she has had 2 falls in 6 weeks which have necessitated a call to ambulance services to get her up again (she hasn't the strength to get up, her legs are very weak).
She had a few falls prior to that but has always been able to get up of her own accord, just. She has a frame, but due to the Alzheimer's she forgets to use it - and also forgets to use her pendant to call for help when she's on the floor.
There has been a couple of episodes of "wandering" (not far due to her limited mobility, but she falls in the corridors and could end up on the stairs as she's 1st floor). The housing manager at the apartments is now leaning on me to consider residential care for her; I also had a call from the community nurse to see what I was doing about a care needs and a mental health assessment, as they had been informed that paramedics had to attend to her for the second time in 6 weeks. 
I guess it's time now she's not safe - I have carers going in for an hour in the morning and evenings, but if she fell at 9pm and forgot about her pendant and pull cords, she could be down all night. I feel a bit overwhelmed by what to do next. I've started by shortlisting my 5 favourite/highest ranked homes speclialising in dementia and Alzheimer's care near me - cost isn't really an issue, mum has income and spare cash plus the value of her flat, so there's enough to keep her going for a bit more than 3 years at £1,000 per week. I haven't factored in what will happen if the money pot expires before she does, but realistically I don't expect her to outlive her funds. It's possible I suppose, but I thought I read that the life expectancy of someone diagnosed at 79 was around 5 years, and we're 3 years in.
But how do I tell her? I was planning on suggesting that she have a couple of weeks of "respite", like a lovely holiday, while she gets her strength back, and just keep telling her that - she'll soon settle in, I hope. I did that when I introduced her "home help" after her first bad fall in the summer - she wasn't keen on people coming in, but I said it was only temporary, and she soon got used to it and is fond of the carers now.
She asks me even now when she's going home because she doesn't recognise her flat as home anyway! I adore mum and we're very close, this post may come across as cold and practical but that's how I'm keeping it together.
MN wisdom and experience welcome.