Nords, your daughter is truly fortunate to have you and your wife give her such a thoughtful upbringing - and much of it by example!
The 18's and 19's and upward are really tough years for parents. They "should" be old enough to do certain things, yet sometimes they act like 12 year olds. It's funny to see some of the reality show kids this age - they all do so many of the same things in terms of behavior it's scary.
The best thing I've found is to do a few things:
1) share the guideposts and potholes like you say
2) sit back and let them make the decisions
3) make them suffer the consequences
Which it seems like you are doing so well. It's prob just the disappointment of your own expectations - but you seem to be acknowledging and mourning the loss just fine!
She will be so much better off for having you and your spouse as parents. Just let her realize it now on her own!
BTW, the budget of her stipend plus your $90/month is not a lot by any means - if she is getting by on that - she is already a frugal genius!
You might want to focus on her great accomplishments this first semester - moving far far away from home to a totally different environment, transitioning to college, making new friends...many kids don't get thru that part well.
and make sure you acknowledge them to her before she goes back - I'm sure she's felt your disappointment (verbalized or not) and I'm sure your opinion of her means the world to her whether she lets you know that or not!
While I'm a big fan of genuine feedback in real time - I've learned that positive reinforcement of the "strengths" and other things goes really really far too...
If i think of something clever to say, i'll put it here...