My mom passed away 9 days ago may she R.I.P. :( My oldest sister asks her daughter to call me...?

to ask me to write a letter of agreement for cremation and in a separate sheet of paper a copy of my driver license and for me to fax it to her fax number at her place of employment. I asked her to please give me the contact persons name and fax number and I would fax over the agreement letter and I.D. to the appropriate agency that is handling the cremation. She got upset and insisted that I send it to her office fax number. When I refused and asked her again to give me the agency's fax number she told me that her mother will forge my signature. It's been two days and I have not heard from my sister or niece. We live in different states. I flew from my state to my moms state to be with her until she passed away. I'm at home now. Please tell me what you think about this and what should I do. My sister is going to forge my signature on the cremation agreement without giving me the opportunity to sign and send the agreement myself. Please reply. Thank you. Brokenhearted.