I agree with WTFMusicPerson. I just told my friends who want to read my stuff that I write gay stories. If they're fine with it, then they can go ahead and read. If not, I have some other stuff that aren't slash. They're fine with it. If she's really your friend, she shouldn't really care what kind of story you write.
But, if you're still not ready to show her your stories. Just do as suggested by playthings.
You could warn her ahead of time what it's about and see if she changes her mind and if she acts strange about it just pretend and be like "lol well I only did it as a fan request" or for a contest or somthing ya know?
Or if you want to avoid it all together change one of the characters in to a girl? Or show her one that's not sexual and is just gay love.
Just tell her you're at a point in your writing development where you're not comfortable sharing it with anyone because you need to figure things out yet. She should respect the fact that you're uncomfortable with lending out your writing if she's a true friend.