First of all, everyone has been in a situation like yours. Not knowing what to do, when you like a girl!
how old are you?
If this girl is only your friend, why the hell, she didn't just answer to your question? Does she have a boyfriend? How old is she?
Before making conclusions, I'd like to know a bit more.
The easiest thing, you could have done, is answer point blank that you saw her on facebook and wanted to know her or get in touch since she is her friend too.
Now that you said you wanted to talk to her in person (I believe you are referring to your friend), you have to say more than that.