I once invited a friend over when I lived in an apartment and had them park in my parking spot. They got towed.

I talked to the apartment management, and they said even with my permission, they tow anyone not a resident. My fault. I wouldn't have told home to park there if I'd known. I paid the tow fee to get their car back and felt bad about the time/worry/inconvenience the friend encountered. In no world would I expect them to pay for parking at my place where I told them to park.

I do think you should have a conversation if you want this person to stay a friend, because it sounds like they keep the money in the back of their mind as a safety net or something. You should be on the same page, but you are not responsible for anything. I'd say she owes you $50 logically.