Sibling (21) asked me if I am autistic in a insulting manner.

I (23) was preparing dinner for both of us the other day and I asked her if she wants me to make her pasta. She said "sure" and I sarcasticly copied her way of saying. This a way of kidding of our grandfather. He used to joke around like this when he asked us if we want something. So she is familiar with this type of joke but for some reason she took very deeply and stared at me for sometime and asked me if I am autistic and she was very offended! I approached her and asked why is she offended this much and asked her if I said something bad and she went silent. I turned around then said "and you are asking me if I am autistic?". She was mad the entire dinner afterwards. Don't get me wrong I am %100 against using autism as an insult. I'm actually worried if she is really autistic or not.

She has always been like this. She doesn't understand jokes %90 of the time unless the joke been said is common. She is pretty unapproachable, lacks sempathy, has social anxiety and have a small friend circle. She goes to public events like weddings, bbq and such because she says it "benefits" her to get free food. Not just to me, but she is like this to everyone including parents. I don't know how to handle her anymore. I always try to bond with her but every single time she gets offended by something that is socially pretty normal she starts insulting me and hates when I correct her about something. If you ask how I try to bond with her, just normal sibling things. Like sharing food, offering to do house chores, go to supermarket, cooking, going out together etc. She hates to help around the house too. She doesn't even want to put fork and spoon on the table.

Any advice?