Does vowing to obey one's mother in everything, save for what angers Allah, conflict with a daughter's desire to donate a portion of her salary after her mother has refused that?

A vow (Nadhir) is disliked (makrooh). Obedience to parents is in what is good (ma'roof), not in disobedience to Allah or in what harms the child without benefiting the parents. If they command one to abandon recommended acts (mustahabbat), then if they have a valid reason, obedience is obligatory; otherwise, it is not. This is because the obligatory obedience to them is in what is good (ma'roof), which is what is permissible and legislated.