Hi! I don't know much about AU rush, except that it is competitive and that getting a bid as a sophomore is tough. With that in mind, I would recommend that you have your daughter sit down and really think about the house that offered her a bid through COR. Have her think back to rush and think about the things she liked about the house and see if she could picture herself being a member of the house. Remember, she didn't get to meet everyone in the house during recruitment. Panhellenic total is 175, our chapter there had 191 in the spring, I say this not to scare you (or your daughter) but to emphasize that she only met, during recruitment, probably 1% of the houses.
I truly hope your daughter thinks and does decide to give the chapter a chance. They saw something that they wanted in your daughter as a sister of their chapter, that say's alot!
Remember, things happen for a reason, and your daughter not bid matching but receiving these bids could be a sign.