You do need to know why, so I think that some kind of contact is necessary, not to beg, but to gather info and show concern:
1) does she consider group work to be wasted time and therefore a waste of tution expense?
2) does she have a behavior disorder (anxiety/panic) that is exacerbated by group interaction?
3) is there someone in her group that makes her uncomfortable?
4) did she receive a text message about a family member who died?
The list could go on, but until you have the right info, it is hard to make a judgement… >>>