Full And Final Compensation Issues

Hi,
One of my friends had served notice period of two month as per the offer letter. 45 days after last working day ,company is not paying her one month salary by giving excuse as there are some issue found in her work (some part of salary and exp letter is already been provided ) . Please suggest any way by which she can take as salary as she had served notice period provided knowledge transfer properly.
Her company replied that your salary is subjected to resolving the pending issue.As she is not a part of that company any more do they have rights to say so

She can claim the amount by sending a legal notice first. If salary is still not paid, she she can approach appropriate forum to recover such dues. Please provide more details like the nature of company, it's state, nature of employment, tenure of service etc. to get better response.

Has she discussed with the company the problem and what needs to be done to resolve it ?
What is she doing to ensure that the problems are cleared ?