A female employee is threatening me for mental harassment after she was terminated from job

I am a director of the small company, with 7 employees, In January 4 2018, I had terminated a female employee, who was appointed 2.5 months back (16th October 2017) because of her poor performance and ill behavior with me and all team mates. As per appointment letter I can immediately terminate her if her performance is not found satisfactory or her behavior is not found good for the company. Also she was on a probation period. I also have paid her all salary upto last date and got receiving for the same on salary slip, also provided her experience letter as she asked for. Now, in april 2018, when I received email from the company she joined for the feedback about her performance and reason for leaving.., I did not responded to that mail, thinking not to make any trouble for her and let it go, but her boyfriend is forcing me to give her a positive feedback, and threatening me if I don't do the same they will file Mental harassment case or any other case against me.. I am so much stressed, being a businessman who do not want to step in any unnecessary legal things, to waste time and money. Please advice what should I do