I think if it felt right for you to tell her, you did the right thing. If that was me, I would have told her too since it would be kind of wrong not to. It’s your dad with your sister, it would be way more awkward not to tell honestly in my opinion, I wouldn’t care what my mom would say. All I’m saying is to let that person know would be better than leaving them in the dark, then let them decide what they want to do.
What if her mom and her biological dad has something to do with her big sister purposely dating her biological dad and the mom was mad because she ruin the plan and what if they had a plan they had to do with the biological dad to date your big sister what if they had a plan for that but she ruined it what if they just previously planned the whole thing wouldn’t that be crazy cause that’s not her biological dad
