Sometimes hernias can be sneaky, but they usually are pretty straight forward to diagnose. If she holds her breath and bears down, there should be a fairly obvious bulge that is visible or palpable if you hold your hand over it. Often, hernias do not cause pain, so pain is not a primary symptom.
Abdominal pain can be caused by a variety of things. It could be she pulled a muscle during her workout (happens to the best of us). It is not uncommon for folks to get a bit too aggressive in their workouts and not gradually build up.
She could have even have torn an adhesion internally and there could have been a little bleeding with it. That would cause pain, but it should gradually get better if it is that.
Then again, it could be entirely unrelated to her workouts and the exercise just brought it to light. So, the wait and see approach makes sense. Give it a week or so, then tell her to go ahead with the weights, but to take it nice and easy!
Jan