A: Your mother's marriage would be valid, if she got married after the `Iddah (woman's prescribed waiting period after divorce or widowhood) i.e. four months and ten days after her husband's death or after giving birth if she was pregnant, regardless if she mourned your father's death or not.
However, if she did not mourn during the period of `Iddah (Part No. 20; Page No. 486) intentionally while being aware of the legal the ruling, she committed a sin and should repent to Allah. If she was ignorant of the ruling, she is exempted from blame. If she married before the `Iddah went by, her marriage is invalid. You have to refer to the court to check that. May Allah grant us success. May peace and blessings be upon our Prophet Muhammad, his family, and Companions.
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