Don't be mad at the woman for gaming the system.
Be mad at the guards who allowed the game to get played.
I work in a building in central Manhattan where, in order to enter the building, you have to show your work ID. If you lose or forget it, they call the floor where you work to confirm you didn't just get fired the day before, then give you a day pass sticker that will get you in the building, but since your ID is magnetized, you're constantly relying on the kindness of your floor's receptionist or other coworkers to get you from your floor's lobby through the security doors to your desk or office. Security isn't that hard to enact in a parking lot, if the guards are of a mind to give a crap. The security guards could ask to see the ID and make sure it's still a valid one. That they would choose not to leads me to believe that either a: they're too lazy to care or b: Disney has decided this isn't a measure worth pursuing or a problem worth solving. As others have said, maybe they hope if you're in the park, the money you're not spending on parking will be spent elsewhere.
I'd be might peeved if I were staying in a resort where parking couldn't be found because of this, though.
And of course, there's always the possibility that the mom who told the OP this story was just B.S.'ing. Some people do like to tell fibs to see if people will swallow their line. My best friend growing up used to enjoy telling people that his uncle was KISS' road manager.
