How Should I Handle a Relieving Letter Request When Exit Formalities Aren't Completed?

I am working with an educational group. One of my staff members resigned a year ago and is now requesting a relieving letter. However, as per the terms and conditions of employment, she did not serve the notice period and did not complete the exit formalities like settling any dues. I need to send a letter to request her to complete her exit formalities before a relieving letter can be issued.

You have no legal standing to ask for the notice period or not having completed the exit formalities after one year has lapsed since resignation. The staff has the right to demand a service certificate.