I know at the colleges around here, if you get a ticket from them it doesnt matter since its not affiliated with the city. If its from the city they can take your license, but from the campus police you dont have to pay but if you get 3 then they boot your car.

Fight it. Campus Police are tools. Rent-A-Cops. Take lots of pics and go to court and DEMAND the school paint the ENTIRE parking lots with new lines and new dividers and post new handicap signs where they need to be.

I doubt you really have to worry about it unless your mom's car is somehow tied to your sister. ie: they have the plates on file for an on campus parking permit.

If that's the case, and you don't pay they will most likely hold grades or shit like that until it's paid.