You are not the one acting immaturely. She is. In fact you are the most mature one in this situation since you even apologized after not necessarily doing anything wrong. If she felt like she was ready to get to the next level through her online messages, then of course that is what you would expect when you meet in person. I think you should let this one go for a bit. Soon she will realize where she went wrong. You don’t need to feel guilty about it or get caught up in her BS. She’ll come back to you if its meant to be.