Are you guys intimate already (are you screwing her or getting blowjobs)? If so, it's a short trip to the fetish fun factory. Just tell her she's hot and how much you love the hair. Introduce the concept that cum is the best hair conditioner available, not something to say "eeew" about.

If not, take it slow. I'd work toward "regular" sex first or a blowjob depending on what is her interest. And make sure she gets her share of orgasms. If PIV doesn't get her off (and believe me, a lot of girls don't) don't be afraid to simulate her orally, with your fingers, or borrow her vibrator. Ask her what her fantasies are, and try and accomodate those too.