I do not practice in Pennsylvania, but I can tell you what I would expect a client to face in Wisconsin. An underage drinking charge in Wisconsin would be a ticket, that is, a civil violation that would result in a fine, much like a speeding violation. It would not result in a criminal record. The underage drinking violation would be something that would be handled in municipal courts, and each jurisdiction, or town, could potentially be very different. In some areas, the may be more than willing to let this kind of ticket go with a fine and some community service, "hold open" the charge until the fine is paid and the community service completed, and then dismiss the ticket at that point. That would result in no blemish on my client's record.
Even if it is a crime, there are still some provisions in many jurisdictions that allow for first-time offenders to have a chance to redeem their record through a "first offender" program, which works much the same way as the scenario I described above.
What you need to find out is 1) Is this a crime where you live, or a municipal violation (aka a ticket)? 2) If it is a ticket, is your jurisdiction (town) likely to work out a deal with your daughter? 3) If it is a crime, what, if any, programs exist to allow her to redeem her record if she successfully completes community service, or pays a fine?
If this is really the kind of thing that can make or break her career as a nurse, this would be worth your time to hire a lawyer in your area who would sit down with her and break down the options with her.