Is it permissible for a wife to say to her husband, "The boundary of Allah is between me and you," when he refuses to take her with him for 'Umrah, and is her fasting for three days considered an expiation for that?

The questioner's intent with "Allah's boundary between us" is unclear, making a specific answer difficult. However, regarding expiation for an oath, it is not permissible to resort to fasting unless one is unable to provide food or clothing.