She got married with a single witness and no guardian; is that marriage valid?

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Check below answers in case you are looking for other related questions:
She loves him and he treats her orphaned daughter kindly, but their families refuse to let them marry
Why is it not permissible for a Muslim woman to marry a kaafir man

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Related Answers:
Obstacles to a Christian woman marrying a Muslim man
She was a Raafidi, then Allah blessed her with guidance but her family will not let her marry a Sunni man
Ruling on a woman marrying someone who attends Mawlid celebrations and practices some innovations
She loves him and he treats her orphaned daughter kindly, but their families refuse to let them marry
Why is it not permissible for a Muslim woman to marry a kaafir man

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