I hate my mother.....?

I know my mother has the best intentions for me, I really do. I can even see it sometimes in the way she behaves. The thing is, my older sister needs a heart transplant and is very sick and my mother gives her everything she wants and lets her go out and get sloppy drunk and turns a blind eye. When she so much as does'nt see me for a few hours she assumes that I've gone to go smoke weed and treats me like some bad, sneaky liar child. I get straight A's and my older sister fails half her classes but she yells at me when i get a B and doesn't even reprimand my failing sister. Now that things have become very serious with my sister's heart, my mother is very anxious all the time. She's already had a very hard life with abusive parents and other very traumatic things, so she's always been anxious. It's amplified now, and I don't think she realizes how awful she's become. She turns everything against people and is secretly very insecure. She especially targets me, all my family members have noticed. I've wanted a therapist for a year or two now to talk about all this and have told my parents that many times. They say "we'll find someone." but they haven't. When my older sister said she ight want therapy, they hired a very expensive therapist. I know this may be because of her heart stuff but it felt like ****. My mother acts all nice and wounded and sweet sometimes and then is an evil ***** the rest of the time and will ignore me and my twin. I hate her and she depresses me a lot.