Quitclaim Deed: Mother and I owned a house together in South Dakota

My Mother and I owned a house together in South Dakota. In 2002 she quit claimed her half to me out of gratitude for a similar thing I had done for her in the past. It is now 6 years later and she is upset with my sisters and I over family issues. I recently received a letter from her lawyer asking that I sign a promissary note for the value that she quitclaimed. This is the same lawyer who filed the quitclaim for her in the first place. Can I be required to do something like this? it just doesen't seem right. Thank you!