Is it permissible for a woman observing the 'iddah of a revocable divorce to go out to attend a meeting—such as a school meeting for the children—with her ex-husband?

A revocable divorcee is considered like a wife; thus, it is permissible for her to go out and travel with her husband, just as it is permissible for her to go out during the day for her needs. If there is a need for her to go and attend a meeting, there is no harm in that, provided she avoids intermingling and other impermissible matters according to Islamic law.