Please mail a copy of the death certificate and a photo copy of their license or ID if you have it to the DMV.  You can mail that to DMV License Production Bureau, P.O. Box 2688 ESP, Albany, NY 12220-0668.  This will prevent further mailings or identity theft.
Can a refund be issues on my mother's registration fee since she just passed?
I would like to get a refund on my mother's registration fee since she just passed, however, I am not the executrix.  Is this still possible?
How can I receive the refund of my mother's registration fee?
It is possible to request that refund, however DMV will issue it to the name of the estate, so you would have to work that out in a way for you to receive it then.  To request the refund of your recently passed mother's registration fee, you must surrender the vehicle plates at a DMV office and request a transfer receipt, not a refund receipt.  You need to have the executor or executrix of the estate send a completed and signed Request for Refund [1] MV-215 with "deceased" on the form, a photocopy of the death certificate, and the transfer receipt to the address listed on the Request for Refund form.
Is there a phone number I can call to request a Next of Kin form?
You can call the DMV Revenue Accounting Unit for that form at 518-474-0902.
What is the exact purpose of that Next of Kin form?
The Next of Kin form is used if the estate of the registrant is settled.  In that case, the refund is issued in the name of the next of kin.
What should I do if I decide to transfer ownership of my recently deceased mother's car?
You can use PDF [2} MV-843 as the checklist to help you transfer the ownership of the vehicle.
Since my mother has passed, who can issue a refund to her estate for her registration?