Are my prayers, fasting, and all my commitment useless because of my mother’s constant displeasure? What should I do to ease my conscience with her, and is it a sin to supplicate for her death?

Allah's commodity is precious, and Paradise is surrounded by hardships. So, be patient with your mother, suppress your anger, and strive to be dutiful and good to her. Show her affection through words and deeds, such as kissing her head and hands, and giving her gifts she likes, for the Prophet, peace and blessings be upon him, said: "Exchange gifts, for a gift removes ill feelings from the heart." Know that your mother is the middle gate of Paradise, and her right to dutifulness and obedience remains, no matter how short she falls.

Your change in dealing with her will lead to a change in her. So, take the initiative to change yourself, seek Allah's help, and ask Him to mend the relationship between you. Her anger towards you has no effect on your worship, for Allah accepts your acts of obedience if they meet their conditions, so do not succumb to whispers (of Shaytan).

Beware of supplicating for her death, for that is an act of disobedience (to parents). Repent to Allah if you have done so before, and remember that she is the reason for your existence.