Cow, I'm not into this doom and gloom. My basic desire is to be just and do the best that I can (some might call it "cause no harm"). From what I have discerned on these threads, that is your desire, too.
Are you and the niece a comfort to each other?
None of us is perfect. I am not arrogant enough to think that my paltry actions are enough to **** somebody up irreparably.
I had five kids. I wasn't longing to have them; I just did it because it seemed like the kind of thing married people do, and I was curious: I didn't want to miss out on one of life's most imposing experiences.
I was undiagnosed mentally ill for a good part of most of my children's lives. Their dad and I hated each other. I isolated and drank. My relationship with my kids was not so much deep and emotional as it was light and conversational.
In other words, i was hardly the earth mother type.
Guess what? My kids are all adults now, and they are fine. We all get along great now, including me and my husband. My own ****ed-upness and selfishness was not sufficient to warp them.
I think you'd be fine and very healthy for your niece, regardless of your warts.
Roommates aren't always as stultifying as you'd think. It might turn out to be a very good thing.
Don't dismiss the possibility out-of-hand.