That would be a housing expense. Understand that 529 funds can be used for the qualified education expenses of tuition, books, and lab fees. Those funds can also be used to pay for room and board, provided that room and board is in direct support of the education. So the security fee would be part of her housing fee, and can be claimed as such against the 529 funds used to pay for it.
If you work through the education section the way it's designed and intended, you will be asked for room and board expenses. Otherwise, if you "jump around" the education section you may never be presented the room and board options.
