If she remains absent/ does not serve notice period, mark her absent from service without permission or authority. May issue a charge sheet/ show cause and initiate a domestic proceedings and then may terminate the service. (this is time consuming procedure and expensive too)
Otherwise, you may wait for her to serve notice period, if she does not, you make make adjustment of full and final settlement by deducting the notice pay.
19th March 2017 From India, Kolkata
Sub: Your Resignation Dated ------
This has reference to your above mentioned letter of resignation. The same has not been accepted by the Company. You are requested to follow the terms and conditions of your appointment order dated --- issued to you by the Company.
You are, requested to meet the undersigned to discuss the matter in detail to take it forward.
Signature, name and designation
21st March 2017 From India, Thane