In middle school I went to the state chess championship for my year, and did very well. As I remember, all the kids thought it was fun, and not too serious. Some of the parents thought it was a little more serious, but no one made a scene or anything. I played against a girl there, but there weren't a lot of them.
My dad bought me a chess book at around that time, but it wasn't exactly written for a middle schooler to comprehend... more like a graduate student. I never learned to properly annotate games. When I joined the chess club in high school, annotating games was a requirement. You could win a game, but have your win taken away from you if you made more than 2 mistakes with annotation. After winning a difficult game against one of the better players, my win was taken away from me due to poor annotation. I never went back after that. In fact, I have played but a few games since then.
I guess what I'm trying to say is that any talent needs to be properly supported to thrive. The fact that you're here asking questions means you probably know that though.
I don't see a big risk in joining up. If it ceases to be fun, let her stop.
