Amy Dickinson is a general advice columnist.
DEAR AMY: Our daughter is divorcing her husband of 25 years, "Scott." "Maggie," their 18-year-old daughter, is in 11th grade. It seems that Scott has turned Maggie into his new mother/girlfriend in every way but sexual. They cuddle together, dress alike, whisper and giggle together in front of our daughter. They go out on dates, text constantly. The teen has cut herself off from our daughter and believes every bad thing her dad tells her about her mom. Our daughter is not allowed to attend school conferences about Maggie. Scott and Maggie are moving across the country together to be with his family, who are supportive of his plans. He told Maggie she will have no more curfews, can get tattoos, smoke, doesn't need to bother finishing school, etc. She won't listen to anyone else. She shouts that she is 18 and "an adult." She keeps saying that her mom has friends to talk to, "but dad only has me." We think this is emotional incest. If she sees a response from you, she might think twice about ruining her life.
-- Concerned Grandparents
DEAR CONCERNED: It's unwise to throw around the phrase "emotional incest," but this does seem like a severe case of parental alienation.
Legally there is nothing your family can do to prevent this 18-year-old from aligning with her father, moving, dropping out of school, getting tattoos, etc. (although her mother should attend school conferences, unless there is a court order against her).
Pushing really hard will cause this teen to back away with equal force. Turn your focus away from punishing her for her immaturity and twisted perspective about her parents -- and point it toward keeping in touch and keeping the door open for a relationship.
Let her know that as her loving grandparents you love her and that you hope for the best for her. Encourage her to complete her education, and offer your help to achieve healthy goals.