Is the husband's mother entitled to reclaim the gold she gave as a dowry to the wife, and is the wife obligated to return it after it has become her property, and can the husband return its value in cash, and does this fall under the ruling of retracting a gift and the exception "except a father to his child"?

It is forbidden to revoke a gift except for a father concerning what he gifts to his child. Scholars have differed on whether a mother is assimilated to a father in the permissibility of revocation. Some have allowed it by analogy to the father, while others have prohibited it. A condition for the father's (and whoever is assimilated to him from mothers) permissibility to revoke is that the gifted item remains in the child's possession. If it leaves their possession, then revocation is not permissible. Based on this, it is not permissible for the husband's mother to revoke her gift to her child if the gifted item has left his possession.