Will Allah forgive me for upsetting my deceased mother, despite my care for her, my repentance, and my apology? And did my mother forgive me despite those quarrels that occurred?

If the quarrels between you and your mother were mere slips, and you regret them, and you have apologized to your mother and sought her forgiveness, then Allah accepts repentance and forgives sins. Allah Almighty said: (Your Lord is most knowing of what is within yourselves. If you should be righteous, then indeed He is ever Forgiving to the often returning [to Him].)

Filial piety is not limited to their lifetime but continues after their death by supplicating for them, executing their will, maintaining ties with their relatives, honoring their friends, and giving charity and performing Hajj on their behalf.