[That Queer Fangirl]

Just be frank with her. It's best I get it out of the way than beat around the bush. Plus your mom might want to talk about how she feels. You're not the only one who's scared. However, have a back-up plan if she reacts strongly. Maybe talk to a friend you can go to, or a trusted adult. She also might refuse to take you, so you might also talk to a friend who can take you without her knowing, though I don't recommend this highly.
Best of luck!