I made a huge mistake and I need some help please!!!!!?

So there's this girl at school that I'm friends with, and I've liked her since near the beginning of the second semester (February/March 2011) and all my friends were telling me to ask her out and I'm a shy guy so I was a bit of a chicken to ask her out because she always had her best friend with her. So finally, time was getting tight because it was the last week of school, I asked her out on Facebook (huge mistake!!!), and she says no. Her exact words were, "I'm really flattered. But I'm having some relationship issues right now with someone, sorry!". Of course, I still have feelings for her. What I would like to know is, do you think that what she said was true or just an excuse as well as, when would be a suitable time (if there ever will be one) to ask her out again? Please give me proper help and please don't troll.