sister in a top house

My sister is in what is considered a top house. She will be a senior next year. I will be a freshman. She is well known in campus. She has promised me a bid at her house.
1. Can she do that? Really?
2. Could being her sister cause another house to drop me?

I want to rush with an open mind and of course I want the best fit to be in my sisters house. But if it isn't then it isn't.