Board Thread:Episode Discussion/@comment-410526-20160702223237/@comment-26397825-20160703132331

Ruby used her semblance to fly from the evacuation ship back to Amity Colosseum, which shows that it can be used for mid-air redirection. However, it's highly possible that she was very emotionally distressed when she was up against Mercury which may have affected her semblance. Also, she may not have developed her semblance much beyond a speed boost, as there was not as much need to; the speed boost suited her needs, and she was only a first year student. There would be plenty of time for evolving her semblance later.

However, when Beacon was destroyed she could no longer think like this, which would explain the semblance upgrade. It apears to me that her semblance still had her as a physical, attackable form in the early volumes, while this seems to be more dodge based (and seems to allow her to literally scatter as rose petals, as opposed to the petals simply being an aftereffect), so she is harder to hit when using the semblance. She possibly has a smaller surface area when using it, which means a smaller area which people can hit to take her out.