What about now?: AITA for saying that to her?

20F

6 year old sister who is mad disrespectful let me emphasize some of the shit she’s done

• Hits people when she’s angry and expects an apology.
• She yells at me when I tell her no and stomps her feet -she once threw herself in front of a moving car because I said no to a toy ( after I bought a candy that she wanted) -She throws tantrums when she doesn’t get her way and yells at everyone. -She cries for the most tiny stuffs -Sometimes she gotta have something even if she doesn’t want it. -she got kicked out of a daycare for that behavior.

I had to take care of her by myself when I was 14 and she was a couple days old (our mom had to go back to work) and I didn’t want to be a horrible daughter and sister. My mother is the problem. Some days my mother will fight back with her but she prefers to cater to her every need and wants just to not have to deal with her crying. This morning,my mom told her something and she’s got mad. I didn’t know what but all I know is she started hitting me and told me to get out of my mom’s business. I hit her back in her arm once and she went crying to her to get me to apologize. mom started coming at me to apologize to her because she was just joking and she’s hungry (she’s a picky eater, she only likes junk food, I refused to feed her French fries this morning because it wasn’t a good breakfast meal) and she’s doesn’t understand what she did. I said no she’s mad disrespectful, what if she does that to a stranger, will you fight with the stranger to apologize to her too. And my mom started cursing me out saying, if she’s not here then her daughter will suffer, she never did that to me( I wasn’t a bad kid). My grandma came after her and said to her that out of everyone who raised/raising my sister, I’m the one who do the most, and that I’ve been doing since I was 14. So she doesn’t get to say shit like that.
I told her I’m done. I’ll make sure that her daughter gets fed and bathe and clothed but I won’t correct her bad behaviors anymore since she’s enabling them and she’s labeling them as jokes and not seeing them for what they are. I feel like I should at least be able to do this for her as a her daughter. But I’m drained some days I want peace from the kid. I use to want kids but since raising her I said hell no.

AITA HERE?