How can a couple be terminated from employment when one had no involvement?

My son made a bad judgement call and lost his job. His girlfriend, who works at the same place, was brought in and was told that she also had to be involved and was terminated as well. She was so upset and tried in vain to tell them she wasn't involved at all. The employer has proof of what my son did and he is owning up to it but nothing that involves his girlfriend. Does she have any legal recourse?