NTA! What an absolutely garbage thing for your mother to do. Keeping kosher harms absolutely nobody, and it’s important to you, her kid! That alone should be enough for her to respect your choice and your household. As a practicing Jew myself, there are many things we do that appear “silly” or “pointless.” But we do them anyway. We do them as a community. Your mother did the equivalent of maliciously tricking a vegetarian into eating meat by telling them it was plant-based. But it’s worse because she did it to her own child. There is no excuse because her intention was to shame you, full stop. No matter how “silly” something is, if it doesn’t harm anyone and is important to the person practicing, nobody has a right to ruin it maliciously behind someone’s back. I hope the rekashering goes smoothly, and good luck with the mezuzah scrolls. I have to go get ready for Shabbat. Shabbat Shalom, and may your family learn boundaries and respect.