How do you give one of your better friends who is very talented confidence?

Honestly, any person especially a female has confidence issues especially at that age since it's the transition to high school and whatnot. You can't really 'give' someone confidence rather they have to find it for themselves. You can however support her, if she is dancing or whatever just compliment her , otherwise there isn't much else you can do about it, people just have insecurities sometimes and they need to come out of their shell themselves so again just support her and she'll be fine.

I agree with Bricheese. I was about to give the exact same answer. The only other thing I would suggest is to encourage her to continue to dance even if she feels self-concious. You obviously feel that she has a natural born talent for it so tell her so. Dancing (as with singing) can be really personal and expressive thing which can bring out all sorts of emotions and insecurities. Perhaps she just needs to quietly develop her confidence and if that means she only dances in private or when no one is watching, then encourage her to do that. In time she will gain confidence :)