Perhaps she didn't have time at that moment to write out an answer. If nothing else has seemed different or "off" with her, then don't worry about it. If you ARE worried about it because other things have changed then the simple answer is, ask her. It sounds like you are insecure, and if you continue this way you're going to have a lot of trust issues. More than you already do. Don't overthink this. Get it out in the open, and make a choice to believe what she says.