My wife hit our neighbours car once. She immediately went and knocked the door and told them. There was practically zero damage to their car but hers was pretty bad. The neighbour was cool about it as they don't care much for their car.
I take it you know the woman since she is a neighbour. It's maybe not worth ruining any relationship with her by bringing it up. Maybe just mention it to see if she says anything or subtly let her know that you know. She clearly doesn't care much for cars so may resent having to pay up to repair something that she isn't even aware that she did.