How do I get our autistic cousin to respect our boundaries?

Okay so we have a cousin who is a few years older than us right? She’s 28 and currently isn’t doing anything for herself. She’s not working or going to school.
She’s autistic but she can carry a conversation. She is argumentative, rude, obnoxious and she always talks about herself. She has a huge ego and never asks how everyone else is doing. So yesterday we were hanging out with her right? She asked me for an opinion on what boy band do I like the best. I was honest and said I don’t really care for boy bands much. They never appealed to me. She looked at me like I was nuts. She was like, “Seriously? What’s wrong with you? Most girls love boy bands!”
I told her sternly, “Well not me. I don’t care for them and not every girl likes them so get used to it.”
Shexkept nagging at me to listen to One Direction. I like some of their songs but I don’t care for them. She kept pushing me and arguing with me. Then I snapped at her to back off and she’s the one that’s asked and I gave an honest answer. She walked off. Man she’s annoying.
Like when we were upset of when things go bad she would try to be positive.
One time we were in the house with no air-conditioning and then we have to go outside. She said, “Isn’t this great! At least we don’t have to worry about having a heatstroke.” we are just looked at her very angrily. She doesn’t respect anybody boundaries. Then when we call her out, she gets upset and put us. We need to be nice. Hell no! We don’t need to be nice all the time. Then she claims we’re being mean when she’s the one that’s being disrespectful and aggressive. She should’ve been talking about boundaries when she was younger a lot better, so what are we do?

How do I get our autistic cousin to respect our boundaries?
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