Hello, boy am I no expert on this! Lying is very hard for me. I have always told my kids that telling the truth no matter how horrible it might be is better then the consequences of a lie. Loss of trust etc.

I would be very clear with her that it's not okay to speak to you like that. You treat her with respect and you expect the same.

In non-heated moments I would speak to her about stuff that she is doing from a mother's perspective. Meaning, get her to think like a parent just don't give her the answers.

Lastly, kids need a sense of belonging. She doesn't belong to your family and she knows this, be honest with her as much as she can understand. Don't scare her. Help her find other community. Art, theater, music, sports, clubs. Help her to have a good relationship with family members who are safe. Reach out to school mates and friends and help her get involved. It makes a difference. Good Luck. BTW you didn't ask but if I saw someone smear feces like that I would call them on it, make them clean it and call rescue if they got out of control. It's a sick thing to do. It would show how looney she is.

Siblings, yuck, why can't we all deal with stuff the same instead of some sucking up and ignoring the reality? They have chosen different realities. Good luck. You can see this resonated with me.