Is expiation obligatory for one who caused the death of his mother in a car accident due to misjudgment of distance, given that the driver of the other truck who did not yield escaped, and is it permissible to delay the expiation until after Eid al-Adha, or must one begin it immediately while breaking fast on the days of Eid?

The questioner is considered to have caused her mother's accidental death due to her incorrect overtaking. The driver bears part of the responsibility if he intentionally increased speed. If specialists determine that the accident was due to incorrect overtaking, then she is obliged to pay full blood money (Diyya) and perform expiation (Kaffarah (definition)). However, if the killing was shared, she is obliged to perform expiation and a portion of the blood money proportionate to her fault. It is preferable to hasten the expiation fasting, and breaking fast on the days of Eid and Tashreeq does not affect the continuous fasting required for a legitimate excuse.