Should I obey my mother who forbids me from praying the Sunnah and voluntary prayers?

If your mother has a valid reason to prevent you from performing supererogatory prayers, such as needing your assistance and service, then obedience to her is obligatory. However, if she does not have a valid reason, then obedience to her is not obligatory. There are three conditions for the obligation of obeying one's parents:

1. That the command or prohibition is not in disobedience [to Allah].

2. That the parents have a valid reason for commanding the abandonment of a recommended or permissible act, or for commanding the performance of a disliked act.

3. That obeying them does not cause harm to the child. This is because what emanates from them merely out of foolishness and bad character is not obligatory to obey. Some scholars have mentioned that disobedience ( Uqūq ) is every act that causes significant harm to the parent, while not being among the obligatory acts.