Uh, what exactly is the issue even if she did bring them to school? Are people not allowed to take medication at school? What if her parents are ass-backwards and she can't even store or bring them to her home? Do you want your students to get pregnant?
Besides, most likely she didn't bring them to school, as most likely she got them from school (specifically the nurse's office, where young girls ideally go to get those meds if they can't get them otherwise. Although it is possible she was given them by one of the male teachers she's banging too).
Finally, what kind of shit teacher calls her out by name during the class assembly to find the suspect? Hell, even asking them to raise their hand when people aren't truly closing their eyes and can see who raises their hand, is just asking for a naive student to raise their hand and get bullied by everyone. You announce the issue, ask them to come forward after class or after school (maybe even another day), and then if a week or so passes without that you then call out to them in private to ask them to come.