I know it can be done, because I've seen girls with their pubic hair colored. However a google search has revealed a few links on the subject and many of them do not recommend the practice.

http://www.goaskalice.columbia.edu/1889.html
http://www.abbys-sexual-health.com/a...pubic_hair.php
http://magazines.ivillage.com/cosmop...412779,00.html
http://www.myvag.net/fur/

I would say that, if you choose to do it, to take her to a place that specializes in that sort of thing. If nothing else, you could always buy that spray in hair color like they have for Halloween.