Why does she perceive the ADL cards to always be wrong? What is her rationale for not using the gait belt? Was help not available, or did she have a reason for choosing to work alone? There are four primary goals for misbehavior: Attention, power, revenge, and display of inadequacy. Of course, there are a few more goals in LTC: trying to get everything done in a timely manner, trying to meet demands from residents or supervisors that are perceived as unreasonable, etc. What was her underlying goal? Irregardless of what you do with her, I think it would be worthwhile to try to get into her head in order to prevent similar occurrences in the future.
Without knowing all the circumstances, I would probably fire her. I might also consider keeping her part-time as a paid feeding aide or some other quasi-clinical position that doesn't put her in a position of endangering resident safety, but only if you are short staffed. If she really is a persistent danger to resident safety, however, she doesn't need to be there at all.