Is it normal want to be besties with brother's autistic fiance

My brother's fiancé is autistic and seems weirded out by me my mom and my cousins.She is polite to everyone but after she has said hey and talked to everyone for 2 minutes she snuggles with my brother on the couch and that is it.She acts like a dude with boobs.My brother likes it. we are like the same age but she does not act like us at all. we wanna be like besties and squeal a lot and like find out all her deep dark secrets and listen to taylor swift songs and all she wants to watch football with my brother and my dad and drink beer. She isn't very social and she does not like going black Friday shopping which is sad.we tried to come in her room for the fourth of july and give her an ambush makeover after she said no three times and she slammed the door in my hand. Apparantly my brother and her were like kind of doing it.My brothers was pissed we ruined the mood. My grandma thinks were assholes and the fiance is the normal one but who slam someone's hand in the door when they put it in the door so they can keep talking.