Well, I guess it really comes down to do you believe her or not? If you don't believe her, then you don't trust her, and trying to build a relationship without trust is quite difficult. Sometimes our minds have a tendancy to think of the worst possibilities for any situation. The fact that you drove over to her house kinda shows you don't trust her. Maybe she just went over to a friends house for a few minutes? Maybe she stopped at a store to pick something up? She's entitled to stop somewhere on her way home if she wants to. Don't read too much into it unless you really feel like something wrong is going on. You're going to make yourself crazy thinking of all of the bad things she could have done, when it was most likely something completely innocent. Not to mention she is going to feel like you don't trust her at all if she can't even make a stop on her way home without you accusing her of lying to you. Try to take it a bit easy, unless you really truely believe something is going on. And if that's how you feel, confront her on it, but only if you are very sure of your accusation.