I take your point that she probably didn't do it in a deliberate attempt to run anybody down, however the "she potentially could have" is the key aspect for me. As far as I'm concerned, this is why we have laws in the first place - to prevent people from being endangered before it happens.

However, the thing that makes me say "call the cops" is her reaction. I get the impression that she didn't care one way or another whether she was breaking the law, nor did she appear to care whether someone was endangered or not. Had she apologised I would have felt differently.