No, it would not just be her word against yours because there is circumstantial evidence against you. From your description, you were not simply a bystander. Your were involved in the theft. You aided it by providing transportation to and immediate transportation from the crime, a "getaway car" so to speak. Based on what you said, you are innocent of any crime because you did not know what was going on. However, if your friend accused you, the situation would be different.
I can imagine scenarios where she might accuse you, even if she didn't really mean to do that. For example, lets say that on this incident a loss prevention (LP) employee at the store is suspicious of her and you. She goes back to the store by herself. She steals again and gets apprehended this time. She confesses. The store LP employee presses her about this incident. She confesses. He presses her further and asks about you, suggesting you were involved. She says yes, maybe just because she is emotionally distraught and rattled. In fact, people accused of crimes say all kinds of things which implicate themselves and others. Even innocent people often confess to something they did not do when they think the evidence is against them and they want to placate the interrogator.
Now, if that sort of thing happened I am not saying you would necessarily be convicted if charged with theft, but it would not be a simple case of your word against hers. It woud depend on the totality of the circumstances and you would be at risk. In contrast, if she never implicates you, there probably is not enough evidence - from one incident - to convict you.

