maybe she likes the idea of having you there, but can not cope with the reality. visits are different as you only stay a little while and she can probably manage until you have left to put everything back the way she likes it. mum likes me visiting but gets majorly stress when we stay. which makes me majorly stressed. ds has more autistic meltdowns, dd gets more autistic like behaviours, and I suspect that they are not the only ones with the condition...
It does sound ocd like or autism like... (I hate having visitors in the place, I can see a lot of those traits in me)
stress will make it worse for her. her anxiety and need to have everything just so will increase, and this is not good to be around for either your sister, her or you.
yes she probably needs therapy, but she may not want it as this is her way of coping with the world. Until she is ready for that then there is no point pushing for it.
I think you have to accept that she is like she is, there are things that trigger her, and those things include having you both in her house.
she might improve when it is just your sister there. she might not improve until you have both left.
just because she might be ill/have a disability/condition, does not mean that you have to put up with it. You can choose your respoinse, like moving out, or visiting for short periods only, or meeting outside her house.
also, I think that people who have not experienced this sort of behaviour have a clue as to what it does to be on the receiving end of it.
I also think that those who have recently lost someone
are going to react very strongly to what you have written and that is understandable. It is not kind for other posters to have a go at them for it.
lots of people say things in the heat of the moment, when under intense stress and when grieving that they might not otherwise have said.
everyone is human, everyone fucks up now and again,