Is it obligatory for a woman to observe the iddah (waiting period) if she did not adhere to the mourning period of four months and ten days after her husband's death?

If a woman whose husband died did not adhere to the regulations of the mourning period during her 'iddah, she is not required to make up for it. She must repent if she did so intentionally. However, if she was ignorant, or forgot, or was unaware of the death, then there is nothing upon her.