First of all, congratulations on your engagement and your conversion. By converting, you’ll more fully affirm that you are indeed an unambiguous and unquestioned member of the Jewish People, and you’ll get a good adult Jewish education program. For many, the conversion process is truly moving; it’s an immersive experience in many ways.
Now … as for your Christian mother. I’m betting that what’s important to her is that her family celebrate Christmas and Easter or maybe other religious occasions with her. I have no doubt that you’ll be inviting her to your home for Passover Seder, Chanukah festivities, Shabbat meals, and maybe even to join you for davening in your shul.
If such is the case, then why can’t you help her celebrate HER holidays in her home? When, God-willing, you’ll have children, you’ll tell them (in any event) that their grandmother is not Jewish. And then you’ll tell them that out of respect for your mother — a Torah value for sure — you help your mother celebrate her holidays, just as your Mom comes to help you celebrate our Jewish holidays.
Do you think that approach will address your very admirable principles? That is: To thoroughly and fully identify as Jewish, and to honor and respect your mother.
Steven M. Cohen is Research Professor of Jewish Social Policy at HUC-JIR, and Director of the Berman Jewish Policy Archive at Stanford University.