I hope you don't mean that's she's already accepted this money. She can simply tell the executor-administrator of the estate that she doesn't want it, and that person can talk with an attorney about the appropriate document.
That said, you don't say how old your mom is or how much she receives in assistance each month, but a wisely invested $40,000 (not $4k, right?) might yield more than she's receiving on a monthly basis. She might want to talk with a financial counselor about that.
Not sure what the number of kids and grandkids has to do with anything -- at least you didn't say (if she's responsible for raising her grandkids, she had better be getting child support from one or both of the kids' parents).