Legal Question in Family Law in Massachusetts

Unless father is an unfit parent, he is the custodial parent and a court can't change this.

First of all, this is horrible news and I'm sorry.

Secondly, if a mother's health is failing, the first thing I would suggest is that she meet with an attorney to put in place financial Powers of Attorney, a Health Care Proxy, and a Will. The mother can appoint a guardian in her Will other than the father. The court would need to consider such a nomination, but, in the end, a court would likely grant custody to the child's father (is the child's father on the birth certificate?) unless it would not be in the child's best interests to do so.

Perhaps the mother and the father should sit down with an attorney and come up with some sort of plan, perhaps giving the grandmother visitation or some other agreement. Just knowing that the parties are working together or have some plan to deal with the daughter may give the mother peace of mind.