It’s getting to me.. how best to manage?

[Fushia123]

DM 89 just diagnosed with dementia. 2 sisters and I look after her - she still lives in her own home on her own. Daily visits, all appts, shopping, meds etc all covered by us.
2 of us live half an hour away. Daily cover for us is either morning then home and return for tea and bedtime, or afternoon until bedtime.
DS who lives 5 mins away has same responsibilities but pops in and out as distance isn’t an issue. She isn’t really aware or interested in the added time involved for me and my other sister.
We arrange cover a month in advance, sort hols and other commitments, and share the two evenings when carers come for an hour equally.
Local DS had a weekend away last week and I did Sat and Sun full days and have 2 more days to do this week.
Cleaners have just cancelled for this morning and she has visitors coming later. I’m due to go back this afternoon until bedtime and was relying on the cleaners to help get things nice for visitors!
Im feeling overwhelmed at present and have just texted local sister to ask if she can pop in for 15 mins this morning to help. (She hasn’t been since last Thurs.)
It’s the first time that I’ve ever asked for help because she’s local. She is a strong character and I’m here feeling tired, overwhelmed and in need of a bit of support this morning. Really hope that she will do this - she has a terrible reputation for not answering the phone, reading messages and turning data off which is very unreliable for us.
She is taking DM away for a few days this weekend with our brother which is why we two are doing more shifts this week.
Long rambling post - apologies!
Just after some Mumsnet support today. Am I being unreasonable?

You are not unreasonable but I doubt your DS feels she is unreasonable either. It is so draining to care for some with dementia. I really feel for you. I wish I had practical advice for you but I haven't. As an only child all my mother's care fell on me and I am grateful for the friends who let me rant and the daughter who lived locally enough to help out. The only thing I would say is that the lack of support for 15 minutes/half an hour is worth a rant on here but not worth damaging the relationship with your DS. I have friends who have been in a similar position to you where both siblings felt that caring impacted their lives more than the other but realised that their relationship was worth more than an extra 10 minutes here or there.

I'm not saying you don't already appreciate that and I do agree that that extra help when something such as the cleaner cancelling would be a godsend.

Honestly it sounds like all of you are already doing a lot and yes I think it would be unfair to penalise your Dsis for living closer to your DM.
How long has this arrangement been going on for and how sustainable do you think it is? I know you want to support your DM but when the lives of three families are so impacted by the care for one person, then maybe it’s time for that arrangement to change.

Thanks so much for your insightful comments. DS texted back to say she couldn’t go, I rang mum and she said she’ll be fine (!)
I’ve calmed down now and although still anxious about other things, I’ve let this one go.
You are right …… this is going to be a long term situation that is going to need us to work together. I am very grateful that I’m not doing it alone - that must have been much harder.
Thanks so much for spending the time to reply. It’s much appreciated. X

Please look at getting more regular care in for your dm- what you are doing is not sustainable. Does she have attendance allowance etc?
@IthinkIsawahairbrushbackthere like me is a veteran of the elderlies board. She is v wise.