Is it permissible for a woman to fast to make up for missed days of Ramadan with the intention of a supererogatory fast so that she can break her fast if she is unable to complete it?

The wife is not obliged to fast this day, whether as a make-up fast or a supererogatory one. If she fasts it as a make-up fast, she is not permitted to break her fast except for a valid excuse. However, if it is a supererogatory fast, she may break her fast before completing it, even without an excuse.