If/when she's ever nice to you, respond positively to her behaviour and be nice to her.

Lol but this has NEVER happened! When I was trying to mend our relationship, she NEVER tried. She doesn't care about me. She would be legitimately happy if I died.

When she's being awful, walk out of the room.

One instance of her being awful is irritably saying "wait!" when I knocked on the bathroom door and scowling while I'm using the bathroom sink with her (I just had to at that time because I needed to brush my teeth to go to sleep). This situation wouldn't be distressing to most people but since I am so negatively affected by even the sight of her, her presence makes me less happy. In this situation, how would I "walk out" and show her she's wrong? I do try to physically avoid her but I can't help being exposed to her. Just the sight or sound of her hampers my mental health because she has that much of a negative affect on me :(

I also don't confront her anymore because she gets more angry and doesn't change anyways.

Don't tolerate being treated with such disrespect and don't sink to her level.

I agree with you but I'm there seems to be no way to not be treated disrespectfully. Ugh you are so lucky you don't have a unavoidable bitch like her in your life! Ugh I hate her so much and will not be able to cut her out of my life (if I cut her out, I'll have to never see my parents again either)