My mother is a Christian?

My mother, who is a halachically Jewish woman, from the former USSR has become a Christian. It’s bizarre. She went otd about 20 years ago after living mo her whole life. Married a non-Jewish man when I was a kid. We don’t talk a lot but I just learned from my sister that she goes to an evangelical church and everything. There are a lot of issues aside from this between us but how do I even make sense of this?