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If the daughter is 18, then the mother no longer has any right to tell the daughter what to do. And no custody orders apply anymore. At 18, the daughter is a grown up and can do whatever she wants.
So the mother can attempt to tell her no, but it is up to the daughter to decide what to do. Of course the daughter may wish to continue to have good relations with the mother, but not listening to the mother and any consequences of doing so - that is her choice. Legally, the daughter is an adult and can go wherever she wants.
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