Since the child hadn't worn earrings in two years, I'm assuming the parents left them out for a reason, such as an infection, or the little girl didn't want momma cleaning the holes. When my DD insisted on getting her ears pierced she wasn't mature enough to deal with the pain of cleaning, turning the studs, so she stopped wearing earrings for quite awhile, then had them re-pierced.
Hooped ear-rings on a pre-schooler is just asking for problems with tearing -- in addition to the unsanitary condition, lack of parental permission, and on and on and on. I would definitely be finding another preschool unless/until the "teacher" was fired.