Jealousy Support Group
Jealousy typically refers to the thoughts, feelings, and behaviors that occur when a person believes a valued relationship is being threatened by a rival. This rival may or may not know that he or she is perceived as a threat. If you or a loved one may have an issue with jealousy, this community is a good place to start exploring the issue and get support. We're here for...
I viewed your profile - I'm pretty sure that in being a lesbian yourself, you will agree that you can't "change" someone's preference. If she is into guys, than she's into guys. I'm not gay so am only speaking based on my beliefs - but I have always beleived it isn't a choice, it's who you are. You're asking her to change who she is.
I'm sure she loves and respects you as a friend, but not more, so you need to decide if you can handle only being friends with her. If you can't, and it causes you stress, than maybe you should walk away from the friendship. Do what is best for you, as hard as it may be at the time. And remember, you are very young, there will be many more friendships and relationships.
Good luck.