Is this girl uninterested all of a sudden?

Unless you can think of anything you did, I would say that nothing is wrong and she'll start acting "normal" again soon. There are lots of reasons a girl would do that... family or friends trouble, school or work trouble, girly things.. haha, I'd wait and give her a little while and if she doesn't seem to go back to the way she used to act, then bring it up (IN PERSON) and talk to her about it and how you feel.