Books about Grief of losing family relationships, not death.

Hi.

I am having some complicated family issues going on. My sister is no longer letting my mom see her kids. They are still young, and were very, very close to her. My mom didn’t do anything to elicit such a response, so she is in shock, and as time moves on, is clearly going through a type of grief over the loss.

Every book on grief I come across is mostly about grieving those who have passed. Wondering if anyone knows of a book that deals with the subject in a broader sense?

She really needs the help!

Thanks in advance!