How to help someone who is brainwashed?

I met one of my cousins recently after many attempts and she is no longer the same person. Her husband convinced her thar women are good only to have kids and rise them.
She no longer meets anyone from family or goes out beyond groceries. She is staying at home with kids all year long.

He even sent her away with the kids to live near his family in our home country while he is still in USA. (She is USA citizen)

She is asking that nobody interfere but her judgment is not stable from what I have seen.

Can anything legally be done? Meanwhile what can I do to support her?
How to help someone who is brainwashed?
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