Why won’t my autistic sister come out and talk to people?

So she prefers to be alone. I mean how can someone live like that? I can’t be alone all the time! My parents, brothers and I are at the neighbors right now hanging out and laughing. My sister is of course at the house cooped up in her room as usual. We encouraged her to come just she said no and she’s watching a movie. I told her she needs to come out but my dad said we can’t make her come and she’ll come when she wants too. My parents enable her too much. When she was a minor, they pushed her to go out and talk to people and once forced her out of the house to hang with our cousin because dad was fed up with her sitting in the house every weekend and refusing to spend time with us and family. Now that she’s an adult they don’t make her anymore. She’s going to miss out on a lot of things if she always in solitude and routine. She needs to get used to the fact that routines will change and can’t get defensive over it. She’s 21. She should be out there with friends having a good time but she has no friends.

Why won’t my autistic sister come out and talk to people?
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