I used to live in a town that allowed garage sales only a couple days out of the year. Not that unusual from what I can tell. I've seen it restricted in similar fashion in a couple other places.
If she doesn't contest the ticket she might still be able to mitigate the fine. I'd suggest she contact the court where the citation is filed, if it was in fact filed in a court, and see if she can get on a calendar in front of a judge to get the fine reduced.