I'd also say a major down side to using it when it's not necessary is the
Cost!  They cost $80.00  a pop here.
My sis's school didn't have a nurse either but the principle agreed to
administer benadry first and if she hadn't settled in 5-10 mins then would
administer the epi-pen.  Perhaps you could talk to the principle directly?
Good luck.  I know you'd feel much better knowing that the game plan is in
order!!