What is the ruling on my marriage to a Christian girl who converted to Islam, if my mother objects, knowing that I do not want to displease her, and that the girl is in dire need of me as a new Muslim?

It is advisable to try to convince the mother to accept the girl. However, if she insists on refusing, then goodness lies in obeying her and showing filial piety, for women are many, and obedience to the mother takes precedence, as Allah Almighty says: "And your Lord has decreed that you worship none but Him. And to parents, do good." (Al-Isra/23). And as the Prophet, peace and blessings be upon him, said: "Stay with her, for Paradise is at her feet." Obedience to the mother before marriage is more important than obeying her in divorcing a woman after marriage.