Is family therapy helpful

My husband's cousin gave birth at 14 and literally didn't want anything to do with her daughter. And so, we took her in and our cousin moved away and now 22 years old, about to get married. She is not looking to get the child from us since we have legally adopted her but at 7 years old, she knows that she's adopted. We love her like she is our own, nonetheless, but she has been very depressed lately. We consulted with a specialist and family therapy and suggested that we do this once a week. Has anyone ever done something like this? I don't see this happening to us because in my heart, she is my child, not ifs and buts.