Mike,
Please dont take this at all the wrong way. NEVER shit where you eat (dating co-workers or dating same gym people). Who needs the extra hassels. I go to the gym to relieve stress and shit, so no hangups there.
IMO not a great idea for movies on the first date. When you brought her home, is this where she and her child live, if so, not a good idea on her part.
Honestly, dont add her on facebook. If she wants to continue dating, she knows how to find you. If you want, text her tommorow and wish her a Happy 4th. See if she responds. If not wait a few days if you dont text her tommorow. If she doesn't respond, well then Hulkotron was right, she isn't in to you. Sounds like it if she was checking her phone during the movie, or maybe she was making sure noone was calling about her kid being sick or so.
Play it cool and see if she chats it up with ya. If not, plenty of fish in the sea