Blacklisting of an employee

Hello sir my name is Dheeraj actually I had an question regarding blacklisting of employees one of my friend who was working for a firm just got terminated and her boss and her team leaders were saying that she got terminated because say violated the rules of the company and told that the reason for termination is is she is doing side business and sharing price list for her personal customer as per her knowledge she has not committed such things but the employer is not ready to accept her but in the beginning she had asked one of her colleague that she can do this type of Business and we can share 50-50 after that statement but they had not done any such thing but the lady to whom she had offer now told the boss that my friend had as offered like this. Now her boss had called and returned her to Blacklist her and see to that that in future she is not going to get any job elsewhere and he has returned to her that she has to give the information and the data list of her personal customer I need your advise what to do