Is a woman obligated to use a gift given to her by her co-wife—despite her suspicion that it contains magic and ill intent due to their poor relationship—or should she dispose of it to avoid doubt and in application of the Hadith, "Leave that which makes you doubt for that which does not make you doubt"?

It is not permissible to accuse the co-wife of sorcery, and one must have a good opinion of her. Perhaps by her gift, she intended to reward her for a previous kindness or sought to foster love between them. She should return the gift to her and increase her supplications and remembrances. The hadith encourages caution regarding suspicious matters. The default is the co-wife's innocence from the accusation of sorcery.