Try to seem confident when you talk about, and not be overly shy and weird about it. It makes it more creepier to her I think. Also, you might whant to hold back a little on the details. Dont tell her you would love to wrap the hair around your cock when your masturbating. I dont know what you allready told her, but go easy. Start out simple and say something like: I like women with beautiful, long hair. I like the way you look with different hair styles, etc. And leave the word "fetish" out of the conversation

If it backfires, try to look at it as training for becoming more confident and forthcoming in the future. If you never try, you will never figure out what works! Good luck!