Is a woman considered disobedient to her mother if she does not speak to her due to the psychological harm she has endured, and would her good deeds be nullified by that?

The mother's right is great and does not diminish even if she is a polytheist or calls to disbelief. You must endure her harm and treat her kindly, without offending her, not even by sighing, as Allah Almighty says: "But if they endeavor to make you associate with Me that of which you have no knowledge, do not obey them but accompany them in [this] world with appropriate kindness," and His saying: "And your Lord has decreed that you worship not except Him, and to parents, good treatment. Whether one or both of them reach old age [while] with you, say not to them [uff] and do not repel them but speak to them a noble statement. And lower to them the wing of humility out of mercy and say, 'My Lord, have mercy upon them as they nurtured me when I was small.'" You must conceal your mother's faults and not disclose any disobedience she has committed, while always being wary of the resurgence of evil between her and your husband. You must strive for your husband's rectitude. Your mother's preference for your brother in giving gifts is impermissible, but that does not justify your disobedience to her. If her harm becomes severe and you cannot bear it with patience, you may reduce your contact with her to the extent that it wards off her harm, contenting yourself with calling her occasionally and visiting her from time to time and offering symbolic gifts.