There are around 6000 students at the combined Claremont colleges. A group of 200 people in your entering class is definitely small but in reality it’s not likely that she would want to be socializing with numbers of people much greater than that (unless she is a very atypical CS type).
My son is at a small college. It is nearly the exact same size as his not too big high school. He says it feels infinitely larger though because EVERYONE is a peer. He didn’t have to seek out his people…they self selected themselves into the school. HMC will be like that.
Since she’s doing the Mudd overnight this weekend, wait until next week to worry about it. She will know after that where she belongs.