as most of you know, my mom passed away last year. my sister and her three kids have lived at the house all their lives (ages 31, 13, 12 and 9, BTW). she is really struggling with the finances because my mom's soc sec/pension was $2100 a month that is no longer there. i've been renting a 3-level apartment for 8 years at $900 a month. the remaining mortgage on the house is $500 for 12 more months, then it's paid for. it's a 3 bedroom 1 & 1/2 bathroom average house. i would move into the basement. i've been living alone since 1986 when i went to college. our combined income will be close to $75,000 per year, which shold make it easier for both of us.

have any of you moved back home after being on your own for a long time? how did you handle the change ?

Establish rules before moving back in.... like cleaning, cooking personal space, smoking, sex/privacy, friends/get togethers for games... etc.

Make sure you establish for yourself rules for her so you don't feel like a secondary parent, nanny or live in maid and she doesn't feel like you are in "her" space.
She has established a lifestyle different from your own, make sure that it doesn't clash to much with your own or you two will kill each other over a slice of cheese.