Ultimately it's about how invested she feels she is vs. how invested she feels you are. So if she's already done a lot, it's fine. If she drives and you pick up the tab and nothing else happens, it feels like the two of you are on equal footing, which means friends, normally (women want a man they view as stronger than them / an authority figure, etc.). However, if she drives, does a lot of other things for you, and THEN you pick up the tab, it can be okay.
Just remember that it's not about any actual concrete thing (e.g., NEVER pay money, or anything silly like that), but rather about the overall feel of the interaction.