Ordinarily, a married woman should defer to her husband to affix the mezuzot. But if this will cause an unnecessary delay, she should do it herself.[1] A husband may choose to share the mitzvah with his wife, just as he may choose to share it with other persons of honor, such as a revered rabbi.[2]
Incidentally, a mezuzah can be affixed at night.[3]
[1] Sha’arei HaMezuzah 16:6:13.
[2] Bei’ur Halachah 135 cited in Agur B’ohalecha 17:39.
[3] Mezuzot Beitecha 289:3; Sha’arei HaMezuzah 16:15.