Gah. I'll be joining a very intensive BA in music program next year, I'm super exited for it

BUT: My best friend (who can't sing to save her life...) wants to join too "because it'll be fun to do it together". How do I convince her not to join? I don't want her to be in my ensembles! Not only is she not suited for this program, she obviously doesn't see this as seriously as I do... I need this BA for my career advancement, not to play around.

Help!