From what I've read, $500 seems extreme given what is reported in the story. I understand that she could have lied but I tend to give people the benefit of the doubt. It seems like an honest mistake so I'd be inclined to show some mercy. And making her pay $500 instead of $1000 fails to show sufficient mercy and still seems rather extreme punishment that doesn't fit this particular crime.
Does she have any recourse? Is there at least court date to contest such a fine?