What if back ground verification gets failed done by MNC ?

Hi, My friend recently got selected as corporate HR in an IT MNC. She has got a good experience in recruiting i.e. for 3 years, prior to this company she worked in US consultancy firm for 1 year and before that she worked for more than 2 years.However, her first company was a consultancy and she worked there for only 3 months which she mentioned in her resume while she interviewed in the current company. Now.... the matter is, she left the first company without serving any notice and now her current company is making an issue of this as first company has given the negative feed back that she is absconded and her salary is due on us. Now her current company has asked her to settle this matter and submit the reliving letter within 20 days. But the thing is first company people are denying to settle this matter and provide the reliving. The fact is... she is ready to pay one month salary which they got agreed upon at the time of employment which is around 12,000 Rs but still they are denying by saying we can not do anything in this and you are just wasting my time. On the other hand, this is unethical as they are doing this just because of the thing happened 3 years back, however as per law, an employee can ask the employer to provide the reliving letter any time as this is the right of employee and providing the same to the employee is the duty of the employer by clearing all dues. Now, please suggest me how can we fight in this case legally to take the reliving letter ? Yashraj Singh New Delhi