Thank you for trusting your question to JA today. I am a licensed attorney with over a decade of law practice and over 20 years of experience in the legal field. I’m happy to be of assistance.
I'm not really sure that I can answer your question concerning her reason for not reporting the issue before. We're just guessing here, but it seems fairly clear that this complaint was made in retaliation for your having suspended her.
Now, all that said, in employment law you can legally be suspended or terminated at any time, with or without cause. This is called at will employment and without a contract of employment that changes that status, you are an "at will" employee.
That means that the employer can entertain this person's complaint, keep you in the dark and not include you in the investigation. There is no due process requirement for a private employer, as they are not a court. You may very well be in a situation where you are being set up, completely legally. Unless you have some evidence to suggest that the actual reason is your race, religion, gender, age, disability or recent medical leave use, you wouldn't even have any recourse to stop it.
I wish I could tell you differently here, but most people don't realize how unprotected their employment is.
If you have any further questions, please let me know. I invite follow up questions, so use REPLY for those. If you have no further questions then good luck going forward and please do not forget to rate my service with a top-three rating so that I receive credit for working with you today. Please rate me based on my service and not on your satisfaction with the law, which I am not in control of and I am just reporting to you. Also, feel free to request me in the future, if you have questions concerning a different matter.