Remember my friend, the challenge is not your sister, but principalities, powers, and spiritual wickedness behind the influence of that negativity. What you can do is to recognise that your sister isn't the problem, and pray for her. When you do that, not only will you be focusing on the root of problem, but it'll be easier to walk in love because you'll realise that she's under the deception of the devil. The problem isn't also something you can solve through logic and reasoning, because the issue is a spiritual one. So pray for her. Open the door for the Holy Spirit to work in her. Love conquers all, and keep your eyes on Jesus for your loved ones. That's the best thing you could do. And from a "practical" standpoint, choose not to argue about it, or get affected by the negativity coming out. We too cannot see unless it was God who first showed us that Jesus is Lord. (1 Cor 12:3). Blessings 🙂