My sister said I'm making her look bad Update

I'm not going to my sister's wedding because she said my son who is 15 and autistic can't come anymore. Her reasoning was stupid. It was for no other reason than he has a speech delay. He has picked up on words and phrases. He calls anybody who is an older man or women that he likes mom or dad. And he says I love you to things or people he likes or wants. So for example. If he wants a slice of wedding cake he would most likely go up to the cake and say to the cake "I love you". My sister doesn't like that and played it off like she doesn't want people to judge me. But then told me my kid is slow and he can't have any actual conversations with people at the wedding. My son is very well behaved. If he gets overstimulated he usually tries to take a nap but he is very well behaved. She's having children at her wedding. Children that aren't so well behaved. But because my child has a speech delay and can't have adult he's can't come. I told her I'm not coming to her wedding and to the people who did say she deserves for her day to be perfect.... She's allowing kids. How could that not potential ruin her wedding but just because my child can't really talk that ruins her wedding. All I understood is she's embarrassed of us and I will never allow my son to think he's an embarrassment or that people should be ashamed of him. Well my mom reached out about the wedding and I told her I wasn't going and she asked why and I told her the truth and what my sister said. My sister called me an hour ago on her fiancè 's phone asking why did I tell people that and I said I just told mom and she said well mom told other people about that and I said "Ok?" She said "Why are you making me look bad". I laughed and said "If I can make you look bad using nothing but the words that came out of your mouth, maybe you should think about the things you say. I didn't even tell them you called my own nephew slow. I told them I wasn't going because YOU said my son couldn't go and I told them YOUR reasoning. If that makes you look bad that's on you". She tried to yell at me but I hung up. So my sister can have her perfect day. It's her day. It's just not gonna involve me. And nothing to do with her will ever involve me again because my son is not an embarrassment. My son is not slow. And he will never be made to feel like that by anybody. And if people ask why I didn't come I will say the truth. And like I said if the truth makes you look bad ......

Update: My sister's fiancè reached out to me privately to apologize and he said that this is my sister and he has no issue with my son being there and that she invited people who don't matter that he feels she's trying to use their wedding as a chance to impress people who don't matter and feels like their wedding has become a promotion more than a wedding. But he said he will be sending a piece of cake home with my mom for my son. I thanked him for the apology.