Going by the facts that you have stated, I find misconduct on two counts viz, (a) forging the leave application and (b) proceeding on leave without approval.
Notwithstanding her misconducts, you have shown unwise haste in her termination. You should have allowed her to resume her duties on completion of her unauthorised leave then should have issued show cause notice to her. If the reply to the show cause notice were not to be found satisfactory, you could have ordered domestic enquiry. Depending on the outcome of the enquiry, you could have awarded the punishment which could be termination from the services.
Sending a message on the phone is not the right way of termination. Just because the employee did not follow the rules and regulations does not mean that we also should give short shrift to the rules and regulations.
Even now also you can order a domestic enquiry on the incident that took place in your company on 7th Mar 2019. Creating scenes or using vulgar language are sufficient grounds for her termination. However, please ensure that you follow the correct procedure while executing the domestic enquiry.
Termination has to follow principles of natural justice.
There is no way that any employer can say-you are terminated- and get away if the employee chooses to fight legally.
Issue a SCN to the lady, seek her explanation, weigh it against evidence-documents etc show her the evidence against her and then take a reasoned decision.