Minor over 18 but under 21 possession of alcohol found in card unopened.

Having high beams on is not a valid reason to search your daughter's overnight bag. Therefore, if the search was illegal or without probable cause, the evidence seized, i.e., the beer should be inadmissible.  Looking to the brighter side, If he didn't cite her at that time probably nothing will happen. It's the prosecutor who decides whether to charge her with a criminal offense. At this point in time; I wouldn't do anything to arose the government's interest.  At this stage of the proceedings, it should not appear as a criminal or Department of Motor Vehcicle offense since she hasn't be accused of any violation of the law.

I hope this information is helpful to you. I don't believe you have anything to be concerned about.