From: Rabbi Moshe Sofer
To: Rabbi Yaakov Baruch Frenkel
The Chasam Sofer rules that a woman may not travel to a bris milah without her husband's permission even when her onah falls adjacent to her tevilah night. The Talmudic exemption for departing on a mitzvah applies only to the husband's departure, since the wife's yearning is derived from the husband's leaving, not vice versa. Moreover, a married woman's obligations to her husband supersede even kibud av va'em, and certainly an ancillary ceremonial role that can be performed by another person.
Source: Shu"t Chasam Sofer YD §162