If she's never experienced it before... your girlfriend is in for SUCH a treat! My first time with a woman wasn't until I was 25 - but I've more than made up for lost time in the past five years. *wicked grin* I love being with another woman. All our curves and softness, the way our bodies respond to touch... delicious! And threesomes are even better. All the best of both delightful worlds!
I'm lucky in that my girlfriends and boyfriend are happy to indulge me when it comes to brushing/stroking my hair and some good hard pulling during sex. My gf's mostly do it because it's such a turn-on for me but my guy enjoys it as much as I do. (I wonder why you see more men than women who have a fetish for very long hair?)