| | worried
First of all, there's no sense in worrying now about something you cannot change either way. You will never actually have proof because you were not there to witness any event or conversation that took place between them.
My concern would be the fact that you know she has lied to you about things in the past ( whether big or small ), and that you accept this behavior as simply a part of who she is. You are ok with it, in essence. If you say you are not ok with it, then in all actuality, if that were true, then you would not be with her. Knowing this about her means that somewhere in the back of your mind you will always question whether or not what she says is true, and if you can't trust her words, then you can't trust her.
Whatever level of love or caring that it is that you have for her, she is not there. And if you think you can change her or wait her out in hopes she will eventually get to where you are, then you are lying to you. So you're going to do what???...have that nagging doubt about her honesty in the back of your mind every time she goes somewhere without you or says something? Do you really want to continue to build your hopes and dreams on someone that doesn't even hold you in high enough regard to be honest?