Ejection or restiction to the bench call it whatever you want. The point being that player once they use the "F" word is Going,Going GONE!!!
You have lost her or his respect and they need to leave the game.Otherwise you make it tough on the next official.Also at least here in NY we can be held liable if the player(student) leaves the field without supervision.In that case I would let her staty on the bench with the understanding she can't partciapate in any way with the team until the game ends.