Tatyana you have definitely been down a rough road. I am not as experienced as some of the other posters but I had to chime in "my food for thought".
Based on what you found out about the previous evictions, you definitely have a bad situation on your hands. Starting the eviction process immediately is crucial.
As for K, you should have a lawsuit here worth more then your $400. It seems to me that you not only have the right to get your money back, report her to the State Real Estate Licensing Commission, but should also make official notice to her that any expenses or damages you incur due to her fraudulent activity will be her responsibility and you will pursue any legal avenues available to you to be made whole. You should be able to get your lawyers fees and any damages made to the property returned to you through the court system. Normally I would say the tenant is responsible for damages, but considering the tenants you have, you know you will not get reimbursed; hence your hiring her to make sure to avoid those tenants. When she entered into a contract with you she had no legal right to enter and placed tenants in your property that did not meet your initial requirements. You may have had a verbal agreement to start with, but in civil cases its not beyond reasonable doubt; you have enough email correspondence with her and a lease that she had her name on for a property you own to prove that their was in fact an agreement. I personally would make it my mission to be made whole and I would hold her responsible for it. That is what she was paid for. If she had done anything she was contracted to do you would not be in this mess. Did I mention "Fraud"?
Well like I said, I am not as much of a pro as these folks, but if I were in your shoes this is how I would proceed. Feel free to let me know if I am way off mark here guys.