Apply the KISS rule: Keep It Simple, Stupid. (I'm not saying you're stupid. Just the opposite - you were very smart to get the treatment you needed. But KIS doesn't make sense as an acronym.
)
Rusher: I understand you just arrived at Exciting U. as a sophomore?
rockette676: Yes.
Rusher: So where did you transfer from?
rockette676: Actually, I spent a year at Local Community College, but I transferred here because I really want a 4-year degree and Exciting U. is close to home and has an awesome biology program.
Rusher: Wow, that's so interesting! Oh, hey - here's my sister OtherRusher. She's a bio major too, and a sophomore. You'll probably have some classes together ...
etc.
If you are grilled about why you have a GED instead of a normal high school diploma, etc., just say you had some problems with your health. If the rusher pushes it, just say you'd rather not talk about the specifics. A good rusher won't push it.
Will you be commuting? Keep in mind that some house-operating chapters have a live-in requirement.
Good luck!