I felt really bad when I gave my summer availability for the campground this year, because I needed three weekends off right at the beginning of the season (two of the three are non-negotiable--little bro's HS graduation and standing in a wedding). When I gave the form to my supervisor, I did it personally so I could explain the situations and then immediately told her that after those are all said and done, I had no more conflicts and could work whenever and however often she needed me with no additional time off. I even said that, to go home for the graduation, I only really needed Saturday off if I could work Friday morning and Sunday night.
The point is, sometimes you DO need to ask for time off. Shit comes up; family members die or reach milestones, your class schedule changes, etc. You can, however, soften the blow and sweeten the deal by offering to cover another time in return. And, come on, she's working in a gaddam COLLEGE town. If an employer won't work around a class schedule, then it's just a dick move on their part. Economy aside, if you make a kid feel bad for needing time off for a class, or deny the time, then you're an enormous bag of deuche. Don't want to put up with that type of stuff? Don't hire college kids.