How do you tell a girl that you don't want to be with her without hurting her feelings?

It's just a woman that is a friend of a friend likes me and wants to hang out and stuff, and she's definitely made it clear that she is attracted. But I'm not attracted to her. She's pretty and sweet, but I feel nothing for her beyond a potential friendship. What's the best approach to this situation. The girl is not the brightest, but has decent common sense. I write things out MUCH more clearly than I can verbalize them, would it be ok to tell her over facebook or texting, or is this non-relationship something that should be more face to face?