So... They suspected her of breaking a crime. Who deals with crime again? That would be Mr. Police officer, certainly not some school inspector pedo.
Not really , a school can do certain things on its ground , some of them even have their own police over there to make such things easier .
So in this case if this school had its own little police then obviously there is a chance the police would be trained for cavity searches so no problem there with the bend over bashful we think you are illegally in possesion of substances with intent to supply .