Just ask her out on a real date and make sure you use the word "date' when you ask her out. You're turning yourself into her male girlfriend because you haven't made any sort of romantic move on her. Chatting over FB if not dating and it's no way to judge whether or not she likes you for more then a chat buddy.
Do something with her and then see if she is open to receiving a kiss from you during your "date." Don't tell her your feelings before you've shown her how you feel.
“The willingness to accept responsibility for one’s own life is the source from which self-respect springs.” ~Joan Didion