Question:
Does the husband’s mother have any rights over the wife?
Answer:
No. The husband’s mother has no [legal] right over the wife. However, [kindness toward her] is considered part of social excellence and benevolence. This is something that fosters the husband’s affection for his wife—that she looks after her interests or serves her in simple matters. For instance, when she wakes up in the morning, she says, “May Allah grant you a good morning, so-and-so!” or “O mother of so-and-so!” or “O my aunt!” There is no difference, and this is good.
As for it being an obligation, then no; because the consorting with kindness is specifically between the husband and the wife.