I would only do it if she was on the edge of moving up and didn't have it. But cartwheel just takes some time for them to figure out - very normal. It isn't something I would suggest a private lesson for at the young ages like 4 years old. If they are moving her into the advanced class then it is probably a good sign that she is progressing and they will continue to work with her. I wouldn't bother with a private unless you are approach suggesting one skill or particular fear issue is holding her back. In my experience, privates for "physical" issues at the lower levels, can be frustrating, because it just takes time. I think that in my experience privates have worked best for a fear issue that takes some drills and backtracking to work through, things that are hard to set up in a class or team training session, where the gymnast has to work around everyone else in dealing with the fear or hesistation issue. In those instances, I have seen privates work extremely well in "getting over the bubble" so to speak. Similarly, if it is a physical issue that requires breaking down the more advanced skill into simpler elements and drills. But for something where there's not a lot to "backtrack" to, a root element like a cartwheel, it just takes time, practice and exercises to develop the strength, flexibility, and coordination. It's not something I would suggest a private lesson for.