According to S. Sistani, if a married lady or in iddah, had zina with a man, then they can not get married at all. They become haram to each other.
However, this verdict is based on obligatory basis, according to S. Sistani. Hence, both parties can follow another mujtahid in this issue, who says that they do not become haram to each other, such as Sheikh Mohammad Isshaq Faiyadh.