What is the correct conduct for a Muslim woman upon the death of one of her parents, and thereafter, especially if she feels guilt for not being able to be present at the moment of death?

If a Muslim is present at someone's death, it is sunnah to prompt them to say the Shahada. After their death, their eyes should be closed, and wailing and lamenting are forbidden. There is no harm for someone who cannot stay with the dying person out of fear, but it is preferable to accustom oneself to it. If there is only one person available to perform the duties for the deceased (closing eyes, covering, washing, shrouding), then it is obligatory for them to stay. It is prescribed to recite Surah Ya-Sin to the dying person to ease the departure of the soul and to grant them steadfastness. After death, reciting the Quran for them is not prescribed; rather, what is prescribed is to supplicate for their forgiveness, mercy, and steadfastness during the questioning.