I've been in the same position as this girl, and it's always frustrated me when the guy in this situation can't take a bloody hint that I like him. If you continue to not make a move, she'll think you aren't interested, get frustrated, but move on. If you boldly, up-front, no-way-you can misinterpret-this kind of way tell her you like her and ask her out, then the chances of you two getting together are a lot higher. Sure, you could think "but what if it ruins our friendship?", but you don't want to get caught thinking 20 years from now "what could have been". My fantastic girl advice: tell her how you feel and ask her out.
She looked at you for a solid few seconds, without talking, during a movie. She wanted a kiss.