I knew my sister called CPS on our dad's wife to make her and dad divorce and I kept her secret

My sister and I (I'm a guy) lost our mom as kids and our dad remarried faster than we liked (within a year of her passing). He found a single mom who was looking for a father figure for her kids and he wanted us to have a mother figure fast so we'd accept her easier. But we didn't accept her. My sister and her clashed a lot because she did things that bugged us, like insisting we use a mom name for her and correcting us for not calling her and dad our parents. My sister used to say parent and if our dad's wife was the only adult home she'd say my parent isn't here but his wife is. She did it to bother her and push back against the mom name and parents stuff. It always rage baited our dad's wife. One day our dad's wife told us she'd adopt us and then we'd have to suck it up and accept she was just as much our parent as mom or dad and find a mom name to call her. My sister called CPS anonymously and reported our dad's wife for abuse. It caused a whole lot of problems and they suspected my sister but I lied for her and claimed it couldn't have been her. I didn't want to lose my sister and stay there. And I also didn't trust that the adoption wouldn't be attempted on me in retaliation. My sister was never sent away and neither dad or his wife ever had it confirmed who called. My sister stopped talking to them when she turned 18 and I followed suit after. We never knew if they figured out it was my sister for sure. There was talk that they might have blamed some of our mom's family because they voiced dislike for the whole mom name and adoption threat too. I look back on that fucked up time and even though I can acknowledge it was the wrong thing to do, I am glad my sister and I could stay together. We're still very close today.