My Dad lost the ability to read, talk, do anything much with his hands and then for a long period the disease caused a certain amount of apathy too, so even though we were quite worried and concerned that he didn't want to do anything, he was quite happy not doing anything. I think the best thing you can do in that stage is to just try to stay positive and upbeat, compliment and praise when they do do something or try to do something, and keep showing them that you love them.
This loss of abilities makes buying xmas and birthday presents very very difficult!
Sometimes too they seem to lose the ability to see photos properly and don't seem to get any entertainment from tv. With Dad it was almost like he lost the ability to comprehend 2D images. Thankfully for some strange reason, after about 3yrs of not getting any enjoyment from TV (and sometimes it even seemed to make him angry) he does like to watch it now, though I'm not sure what he sees or hears. So you could try the tv, because at least that is keeping her in the loop with the outside world to a certain extent. And even if it des't work today it might work another day. It can indeed be a fair bit of trial and error.
Dad also went through a long stage where he was obsessive about sweeping and wiping up the dishes. It drove my mum nuts, but at least he was occupying himself.
Mostly however, it did end up coming back to us to initiate things, a lot of dementia patients seem to like to walk a lot and we always had a theory that it temporarily improved Dad's condition, maybe getting the blood circulating and getting more of it to his brain? I think keeping our loved ones active can be a good idea anyway, as I have found it much easier to cope with Dad because he can walk still, rather than the times he was stuck in bed because that was very depressing to seem him so weak. Them being active however can also have its downside, especially if they are bigger than you and start being difficult.
Music is another thing.
Last but not least, this constant need for you to be there can become extremely draining so it is imperative that you get others involved in her care. Even if they are not carers as such, but just friends or family that can come over and have a cup of tea with her..and better still if you can get people to come over so that you can get out and have some time to yourself. Because in the end, you will be a better carer if you get this very important 'me' time.
Sorry I couldn't be of more help, best of luck,