Cher's Daughter-In-Law Claims Singer Ignored Her Pleas Over Troubled Son

Cher's daughter-in-law, Marieangela King, is fighting the legendary singer's effort to take control of her troubled son Elijah Blue Allman's life ... TMZ has learned.

In new court docs obtained by TMZ, Marieangela claims Cher and her team have refused to work with her in developing a long-term plan for Elijah's recovery and care and have instead "systematically excluded" her from all discussions even though she's his spouse.

As we reported ... Elijah was arrested in New Hampshire in March on assault and other charges. Marieangela says he's currently locked up in a psychiatric facility under professional and state supervision.

Cher is making moves to take over control of her son's life through a conservatorship -- citing struggles with drugs and managing his affairs – but was shut down years ago in a similar effort.

In the new docs, Marieangela says Cher should not be given power over Elijah ... claiming Cher and Elijah have an "extremely poor relationship, and many unresolved trust issues."

Marieangela says she's asked Cher repeatedly to help arrange a workable treatment plan for Elijah … but says her outreach efforts have been rejected or ignored. She claims Cher has used her fame and money to manipulate doctors and other professionals to interfere in her relationship with Elijah.

She says Cher's conduct reveals a "calculated pattern of intentional prejudice, hostility and bad faith aimed at dismantling" their marriage.