Hi there ~ welcome to the forum
Can you tell us how old you both are; how long you have been friends & how this conversation went. Maybe a liitle more information would help us.
For now, I'm guessing that if she liked you one day, then she liked you the next day.
Either she didn't mean what she said & was being silly with you ~ which isn't likely, since she is your best friend, or she did mean it and then felt shy & embarrassed the next day, having changed your relationship from just friendship to something else.
Did you speak to her the next day?
Have you spoken to her since?
Did you tell her that you liked her, too?
Make an effort to be as friendly as you usually are, so that she doesn't feel awkward around you.
If you like her ~ tell her.
See how it goes.
