I know a lot of kids just like her, and several have ended up back in Boulder within a semester of going OOS. My nephew attends, and as you say many see their friends from high school going to Boulder and having fun with friends new and old and think ‘Why am I going to some other school when I could be paying less and going with my friends?’ These kids were upper middle class or wealthy, so the cost of CU was probable a lot less when they switched (no needs based aid, but some merit forfeited when they transferred).
I’d not make her go back for yet another quarterif she’s really unhappy, although I’d encourage her to do so. Some schools don’t take freshman transfers, so she’d need the equivalent of 30 semester credits or 45 quarter credits. It’s also just a little stage when a quarter credit transfers as .75 of a credit, so she could have 5.4 credits of history when she’ll need 6 to satisfy a core requirement. I think CU does allow the transfer, but in the olden days, CSU did not (don’t know about now)