Is it permissible for me to masturbate using my wife's hand while she is fasting and I am not?

Enjoying the wife's hand is permissible. If the wife is observing a voluntary fast, it is permissible for the husband to enjoy her, even if it breaks her fast, because he is allowed to make her break her voluntary fast due to the husband's right. However, if the wife is observing an obligatory fast, it is not permissible to masturbate with her hand or to enjoy her if it leads to her discharge, due to the invalidation of her fast.