Because my folks are really broke-down poor (as is my sister's BFF, who is also not going to be in the wedding due to finances and having an infant at home). They have 1 ancient, falling apart Dodge Neon, don't own a home, barely have a pot to pee in, next-to-no retirement savings. Relative to most of my family (except my brother) we're very comfortable. But money for us is still semi-tight. We spend any "extra" cash on nice bikes, rather than taking family vacations. I'm sure my sister views us as well-off, but we just spend our money differently. Our mortgage is dirt-cheap ('cause we live in a dumb old house, rather than having gotten sucked into more house than we could afford when that was a popular thing to do), but we still live on one income, thanks to MI's especially crummy economy and my unwillingness to spend 2+ hours in my car commuting to make peanuts. We make ends meet and have a little leftover for fun, but that's it.
As far as what I fear she will do...I don't know. She has proven in the past that she will lie to paint people in a bad light. She's on FB...lord only knows what she would do with that medium. I don't think people would believe anything she could come up with, nowadays, but who knows the lengths she would go to.
Mostly I fear that she'll make things ugly within our family and will keep me from seeing my nephews, which would break my heart. I don't get to see them nearly enough because of distance, as is. Her eldest son and my son are very close and her boys are the only cousins my son has.