I would of put her down to if she is as you described. Mantids rarely fall during moulting so I wouldn't worry about it. If you want you could get some kind of mesh to put onto the lid of your enclosure for extra grip. I've only had a couple mantids fall during a molt and they were hanging on the same type of surface all the other mantids molted from. Sometimes it just happens. They usually die or get really messed up if you don't see them right away.