aita for telling my severely disabled sister that the world doesn't revolve around her disability..

So I (15F) have a sister (12F) without legs and arms . she also has down syndrome. recently we were at a party and she wanted to eat cake but the birthday girl wanted to eat first. my sister started crying so I hit her and she went tumbling down the stairs. nothing happened but she started crying and whn everyone went to pick her she said I kicked her down even tho I only hit and her dramatic self just shoved herself down the stairs.

now I can admit I'm not the best person for hitting her. it's just my parents hit me too, but not her.. a little slap on the wrist didn't hurt me.. so why shld it hurt her. after I picked her up I went to near the cake and she forcibly let go of me and jumped into the cake, ruining the party. I brought her to my car and yelled at her. and she said smt along the lines of I don't even have arms and now u can't give me cake. so I told her tbat the the world wont move for her, when she cant move for herself. now my parents are calling me disgusting, vile and an abuser.