Untame-able four year old sister?! Help me please!!!

Hi it's BrokenDST again. I am seventeen years old and have high functioning autism as a mental disability as well as OCD and ADHD. I have a four year old sister named Sophia. Now no matter what I say, do, or think, I always love my little sister because well, why shouldn't I? I've taught her about video games and she actually proves to be quite intelligent during gameplay (ie. she throws my avatar across gaps to help me get across and stuff). She's fun to be around and play with and I wouldn't trade her for anything in the world, even my own soul. There's just one little itty-bitty problem. SHE REFUSES TO BE DISCIPLINED! Quite often my parents will both go out shopping or taking care of business, and that leaves me in charge of Sophia. Usually I'll be on a computer game but mute the sound so I can listen for her in case she gets into something, but half the time, she's so ____ sneaky about it! And I'm someone who doesn't take teasing or provocation too lightly, so it really heightens all five senses if it goes on long enough. She'll act like she's sitting on the bed/couch behaving and watching something like Uncle Grandpa, then she'll wait until I turn to look at the game and I look back, poof she's gone in the bedroom making a mess. And since I'm kind of a babysitter I have no choice but to scold her, used to, telling her "NO" or "stay out of that" would actually work, now I have to resort to countdowns in order to get her attention and if that doesn't work I have no other choice other than to spank her. Even then, she doesn't respond. Then there are times where she acts like I don't even exist, and she'll do just about everything. One time I woke up one morning, groggy and half asleep I tripped over my own foot by accident and felt something sticky and wet, I looked over on my side, the entire wall and her play table was covered in egg yolk, crayon wax, marker felt, cake icing and soda!!! My jaw hit the floor and I had my heart in my mouth and I couldn't even think about what would happen if my stepfather came in and saw that. It had looked like three people and two dogs had thrown up on the wall all at the same time. There she was, smiling away like she had pulled some sort of prank and bouncing as high as the friggin' ceiling! She didn't even stop to breathe! She is like this to this very day and it seems like it's getting worse by the mere second even as we speak; now she's in two new child phases and she's learned about getting physical with me, she's stealing from my backpack and laptop bag, she picks up anything I own and says its hers and when scolding her isn't enough I try just taking it from her cause I don't know what else to do, and she just plays keep away with it. Not only that but now she's started kicking me and hitting me while doing so! I don't know what to do and I'm afraid her scamp-like behavior might worsen the dysfunction in my family! If my parents are around while she's like this I just get scolded when I try to contain her and it's not fair that I'm the one getting in trouble when Sophia's the one acting out this bad and nobody's batting an eye! I don't know what to do to make her behave now and I'm reaching out to ANYONE ON THIS WEBSITE for guidance at all, anything will help! PLEASE! I can't have my own four year old sister grow up to think its okay to constantly fight with one another and act like a crack addicted, meth hopped stunted scamp all the time! I'M BREAKING DOWN AND FREAKING OUT WHAT DO I DO?!

talk to her about this explain her why it is neccessary ,if it gets worst take her to a child counseillor

I've talked to her and explained to her why she can't get into some things but it was no use. One time I had to fence her into the bedroom for time out using our old baby gate. Is it me or is my sister made of Pixie Stix?