I agree with what others have posted regarding this issue. And, not to berate you regarding the "forgetting to lock the med room", but that is a major issue, however, this certainly doesn't excuse your supervisor's behavior. That individual should have had better sense than to do what she did. Supervisors and Managers are supposed to "lead by example", not participate in making the situation even worse. Very, very poor decision-making on her part.
I am not exactly sure where you work, but if you are in a hospital then you should have a compliance department and should be able to contact that department anonymously, to submit a complaint against your supervisor for her behavior, along with submitting an incident report regarding the incident. Most hospitals I've worked at have also had a "no-retaliation" policy as well, meaning that once the situation is investigated, the supervisor is not allowed to retaliate against the employee for turning that supervisor in, for example, by giving that individual a bad performance evaluation or by making things difficult for that employee.