Is the maternal aunt considered sinful for not informing the husband or his family about the defloration that occurred to her niece before her marriage, which she then stitched up, knowing that she concealed the matter for the sake of covering for her?

The woman must repent to Allah Almighty for what she has done, and she must repent from hymenoplasty because it is not permissible except in certain cases.

She must conceal herself, and the aunt is not sinful for not informing the husband and his family. Rather, it is obligatory for her to conceal it unless the husband asks.