Is AUTHOR wrong in the post ? POST : I'll start by mentioning that my (21F) sister (22F) has been diagnosed as bi polar and has borderline personality disorder. She's actively bashing on my mom because my sister used her credit card to buy 10 bras, and my mom asked her for money back. My sister refused and started saying "Fuck you" over and over and telling my mom that she can't live here anymore. That's when my mom said "No actually, this is my house and I can be here anytime I want". This made my sister *furious*. This happened a couple days ago.

So currently my sister is still being a brat to my mom and saying "Fuck you" and sticking the middle finger up at her which is making me upset because I love my mom and she honestly doesn't deserve any of this.

Anyway, we're ordering sushi for dinner tonight &amp; my sister hasn’t spoken to my mom all day (besides just giving her the finger). My mom was originally going to pay for dinner so she asked my sister what she wanted to order &amp; my sister told her 2 spicy scallops rolls (the most expensive thing) and rolled her eyes as she said it. This was also the first thing she said to my mom that wasn't "Fuck you" in 3 days.

So because I’m pissed about this and since my mom isn’t ordering anything, I told my mom that I’d just get sushi for myself and pay by myself and not get my sister anything since she’s being so rude and ungrateful. My mom said no and that she’d pay since she already asked and wanted to keep the peace. 

I compromised with my mom and said I’ll get my sister one roll instead of 2 and I’ll pay for it myself. I told my sister that I’m paying for it so I’m only getting her one roll and her attitude completely changed. That's when she was like,

"Oh OP that’s so nice and thoughtful! Thank you!"

"Don’t thank me, I didn’t want to get you anything. Mom told me to so you should thank her."

It felt good saying it but I heard her mutter "that hurts..." under her breath a few seconds after I told her that so now I’m second guessing what I said.

AITA?