Mistaken identity that resulted in retaliation and "employee discipline"

Question: Are their any legal ramifications when an employee of "good standing" is subjected to "employee discipline" in retaliation for a formal grievance filed within the company's HR by another known employee who asked to remain anonymous? To set the stage – I am posing this question on behalf of my girlfriend who wants to remain anonymous and we shall call her "Kat". Kat has been with this same company for 6+ years and recently transferred to another state in hopes of growth opportunities within the company. As a single mother, Kat always sought the reasonable “approval” for “time off without pay” in advance so as not to use vacation time or sick leave wherever possible. Kat was "written-up" and placed on probation (with the threat of termination) for "approved" Unexcused Absences (UA) after another employee anonymously filed a grievance against their manager to HR for inappropriate attire and vague harassment in the workplace. This unfortunately led to the mistaken assumption that Kat had filed this grievance because of her good standing within the company and her obvious discomfort for the lack of professionalism there within. It is only after the embarrassment and emotional distress from the disciplinary action that she discovered a fellow co-worker had recently filed a grievance against their manager. This was unbeknown to her originally. It is only in hind site that the act of retaliation becomes relevant time-wise. As the employees recall, just prior to her write-up, the manager, along with the use of their supervisor, questioned all the staff including Kat about "issues" with the manager. All would have agreed (except for the anonymous employee) that this seemed out of the ordinary. In hind site, the write-up, probation, threat of termination, and maltreatment ever since, has led us to believe that their analysis concluded she was the culprit and as a result they conceived a process of retribution.