Girls giving the one word answers!? GIRLS ONLY PLEASE?

I am 16 (and so is she) and i got her number at the winter ball. We were both sober and i really like her. The next day we had a nice conversation over text and now she is giving me short.one word replies. I am going to call her tomorrow and ask her out. But why is she giving one word answers? She kinda is busy shopping atm but she gave me a one word reply over text once before that. I am almost certain she doesn't have a boy f otherwise she wouldn't have gave me her number? I just want to speak to her face to face but she was busy so i couldn't call her, so yea why the one word replies, i am sure she likes me as well! 10 points!!! Many thanks guys!