first off, yay for the Beatles!!!
secondly, yay for a very self-aware post and for taking responsibility, not just blaming "the mean sorority girls."
As far as not making it into the colonizing chapter - colonies often look for a different type of girl than an established chapter. You need to be a little "more" - a little more outgoing, a little more committed, a little more confident - especially if it's on a large Greek campus (which I'm kind of guessing this is). If you did have, as you say, a chip on your shoulder, it's not likely you were what a colony was looking for, legacy or not.
If you transfer back to the first school you'll be a junior, and if this is a competitive school, that will have a negative effect on your chances. You might only have the option of a chapter that doesn't make quota. Honestly, I think if I was you I'd stay at the school you are at now rather than transfer back someplace that gave me so much heartache. If it's a specific major that you can't get where you are now, you might be better off to start completely fresh at a third school.
There are a couple stickied threads at the top of the sorority recruitment forum that would be helpful for your sister.