Ebbie, as I looked at the clear sight with which you portrayed your sister's situation I found myself wanting to hear your situation written the same way.
My sis is a sociable person and a woman who is still strongly attached to her own 'things'. She likes to entertain guests, she relishes her friendships. Not only would a single room be bad for her, she would much prefer a two or three bedroom home; she likes to have a room for overnight guests.
I find myself circling around the fact that perhaps you are taking on what you want to prevent for her .... How would your life be impacted once you got there.... You probably will need to go down to assist in finding solutions... but keep looking until there is a bit of sure clarity.
There is always a ripple effect and sometimes it can be bigger than expected. BG....