What is my duty towards my Christian mother who refused to embrace Islam after my repeated invitations to her?

It is obligatory to be kind to one's mother, to honor her, and to maintain ties with her through words and deeds, and financial assistance, even if she refuses to embrace Islam. This is based on the Almighty's saying: "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." One must also frequently supplicate for her and for her guidance, and not despair of inviting her to Islam in the best manner and at appropriate times, and gifting her books and da'wah (invitational) videos specialized in inviting Christians, and communicating with specialized callers to Islam.