Depends on the property. If she works like at a Mall, what the owner's of the mall sometimes do is annex the parking lot or do something like that to the city, therefore the city has the right to ticket people and patrol the property, meaning the mall gets use of local law enforcement (this is not the case for ALL malls or store parking lots). So in that case it might be considered public property… Just a consideration...
They are probably afraid you may back out or something like that and deny anything happened….