I feel like I've opened a can of worms but I think you are leaving yourself very vulnerable big blue.
As your mum is quite a bit older than I'd first envisaged the future may be where she needs full time care.
At just £1000 a month she barely has enough for two weeks stay. Homew where I live pan out at about £450-£500 a week, in other areas then you can add at least another £250 per week.
So, she would need a top up of fees. That comes either from the sale of her home, or from other properties or savings that she might have or from the LA.
If you have less than £23,500 then you can have have help from LA which is where you need to be upfront about mums finances. If your mum would be completely self funding then you don't have to go down this route but as her primary carer big blue which is what you would become should she start needing care you really need that LPA.
Again, I'll tell you why. If your mum loses capacity ie has a severe stroke and is no longer able to control her finances then someone has too. The state can step in or you apply to be your mums deputy . It's a long and very expensive process costing well over £1000 and from that day every penny you spend on your mum has to be recorded and then each year you fill in a very detailed form that you need the brains of an accountant.
I think you need to sit with mum. Get the LPA forms and have the talk. This is what we are going to do blah, blah. Believe me, you DO NOT want to become a deputy. If ever you need to register the LPA it forms it costs £120 and you have a lot less hassle.
LA's have a lovely tuRn of phrase ....it's called deprivation of assets. What your mum does in her earlier years with her finances is up to your mum, but once they get into late 70's and 80's and elderly old age is on the horizon it all becomes a different ball game. You need to protect yourself. Especially if your mum is very generous to your sister. You might need to have the talk with your sister as well.
I know you started this thread as you felt your private time has been eroded but I'm glad you raised it because so many people start out like you big blue and end up in horribly stressful and financially difficult situations.
Some better boundaries in the home might be the answer. Maybe make your own bedroom like a sitting room and say to your mum we are going upstairs to watch a film. Maybe see if there are social clubs mum can go to because if she does start to fail you will be glad of some sort of daycare and at least she will be used to going to them.