When does my mother's iddah end, given that her husband passed away on Dhul-Qadah 25, 1434 AH, corresponding to September 1, 2013, and knowing that the iddah is four months and ten days?

The waiting period ('iddah) for a pregnant widow ends upon childbirth. For a non-pregnant widow, the waiting period is four months and ten days. The day of the husband's death is counted as part of the 'iddah period according to the majority of scholars, contrary to the Maliki school. The calculation of the 'iddah is determined by precisely noting the day and time of death. Whatever remains of the first month is noted, then four full lunar months are counted, and then from the fifth month, the number of days required to complete the ten days is taken, so that the 'iddah ends at the same hour as the husband's death.