My girlfriend and I have been having sex for a while now, but I guess she wants to start experimenting in bed. I'm not sure if it's because she's bored or if it's because she just wants to let me experience more things with her. Recently, when we were intimate, she moved as if to perform oral sex, but I didn't know what she was doing at the time so I stopped her. Later she explained what she wanted to do, but she hasn't tried to do it again after that. I think I scared her from trying to do new things because I freaked out a little.
We're in the US and we are both girls. She is older than me.
How can I broach this subject so that we're both at ease (so that I don't get surprised and she doesn't get dissuaded from future attempts)?