Why didn't she add me on Facebook?

I met this girl at a party yesterday and we talked for a short bit. I really like this girl. And we made a lot of eye contact at the party. She gave me her cake because she was too full and asked if I want something to drink. Keep in mind that she's a good girl...doesn't drink, smoke, clubbing etc etc. She's also never had a Boyfriend ... I just screwed up by not talking to her enough last night. Oh well.

I added her on Facebook... is this a indication that she isn't interested in me? Or could there be a million other reasons why she didn't add me.

I have no other way of talking to her as of right now..since... I don't know her really lol. I only met her through two of my friends (They're together).
Why didn't she add me on Facebook?
Post Opinion