Is Full and Final settlement should be done in case employee not signed the appointment letter ?

Dear Sir, In our organization, one of the employee was worked for 20 days only. We have emailed the appointment letter to her and followed up but she didn't sign and forwarded it to us. We had to terminate her as she was not maintaining any of our terms of appointment. We have also conveyed to her that the 20 days payment will be initiated. Due to delay in F & F settlement as our authorizing signatory was not available, she misbehaved with our director also misbehaved with an existing employee saying, fraud people giving the threat of labour court. What should be done in this case as our company doesn't want to settle her dues due to this misbehaviour at the same same she didnt sign the appointment letter. we have one clause in our appointment letter; 06. Termination / Dismissal The company shall have the right to terminate your services without any notice and / or compensation in the following situations: Major misconduct or disobedience of written instructions given by the reporting officer or higher management., Breach of company’s policy, Breach of security, Unsatisfactory performance, Misrepresentation or giving false statements about personal/professional background or suppression of relevant facts during the selection process or at the time of joining, Involvement in criminal offence, Involvement to breach any policy, Violation of the terms of employment and undertaking given at the time of joining or thereafter, or violation of the service agreement, Medically or mentally unfit, Loss of confidence, Abetting or inciting Others to disobedience or misconduct, Conflict of interests with Company's business interests, 7 days of unapproved or uninformed absenteeism from duty. Please suggest us asap.