AITA for not letting my brothers girlfriend in the family?

Every year, for my birthday party, I always have a very specific dress code to make for cool photos. (My family also usually uses a photo from this party as our Christmas card). For this year, I said I wanted my guests to wear black, my close friends and family to wear white, me myself was going to wear red. For context, I have three brothers. I obviously invited all of these brothers and their wives and girlfriends to the party. Now, my eldest brother is married to his wife for almost five years and they have two kids together. Although I’m not close to my sister-in-law because her and my brother live a few hours away and I haven’t spent much time with her, she’s always been very nice and is obviously a part of the family as she is married to my brother. Because of this, even though we’re not close, she was obviously going to be wearing white. My other brother is not married but he is bringing his (new) girlfriend who we will call Anna. Her and I were roommates in college and she is one of my closest friends, and I was beyond thrilled when her and my brother started dating because I was excited at the possibility of having her as a sister. My last brother has been dating a girl for about three years now. His gf let’s call her Sarah wasn’t expecting to wear white until she found out Anna was going to be wearing White.

Sarah confronted me about this and started telling at me, enraged that Anna was wearing white even though she’d only been with my brother for a few months while Sarah was dating my other brother for many years. I calmly explained to Sarah that I understand why she’s feeling this was but that Anna was not going to be in the family picture that would end up on our Christmas card but was only wearing white as one of my closest friends. Sarah was still mad and demanded to be wearing white, even when I explained this to her. My brother angrily called me and told me that he and Sarah wouldn’t be attending unless Sarah was wearing white. I laughed it off because I didn’t think it was that big of a deal, and ignored my brother’s requests because I was frankly getting mad at this point. It’s MY party and I should be able to choose right?

The day of the party, Sarah showed up, wearing white, and demanded to be part of the family photos that will end up on the Christmas card. My parents are super traditional and explained to her that she wouldn’t be on the Christmas card until she’s engaged to my brother. Sarah threw a hissy fit and at the party and started crying after a conversation with me, making it out to be like I bullied her in some way.

Looking back, I feel I overreacted over the white and should’ve just let her wear it because I honestly don’t even care that much, but I still think it was rude of her to show up in white anyway. Am I the AITA?

UPDATE*

Hi, I’m back with an update, and I’m really struggling to process everything that’s happened. I know I messed up in the past, and I genuinely tried to make things right.
Sarah felt excluded from the family photo and, to be honest, I didn’t handle her feelings well. I was frustrated, but after some reflection and reading through your comments, I realized that I hadn’t been as considerate of her feelings as I could’ve been. I thought I had gone too far, and I felt like I should apologize. So, I called Sarah. I told her that I was truly sorry for making her feel left out. I explained that I never meant to hurt her or make her feel excluded and that I should’ve communicated better. I really wanted to fix things because I didn’t want the tension between us to stay. I let her know that if I ever made her feel that way again, she should just come to me, and I’d do my best to make it right. She seemed to accept my apology. She said she understood where I was coming from and that she appreciated me reaching out. She even apologized for the way she’d reacted. It felt like a huge weight was lifted off my shoulders. I thought maybe this was the start of rebuilding a healthier relationship. Afterward, I wanted to show her that I wasn’t just saying things to make peace but that I was genuinely trying to include her. So, I took a suggestion from one of the comments and I just booked a family photoshoot with the photographer we’ve used in the past, and I invited Sarah to join us. I told her that I’d love for her to be part of the photos because I wanted her to feel welcomed, and I wanted to include her as part of the family. I thought this would be a nice gesture, showing her that I was serious about making things better. Sarah seemed grateful for the invitation. She said she appreciated it and looked forward to being included. I thought, “Okay, we’re getting past this.” I really felt like I was doing the right thing, making up for the tension, and trying to mend the rift between us. However, one of my friends brought to my attention that Sarah posted something on her story along the lines of that some people fought her to keep her away, which I ignored because it could be about anyone. Then she made another story where she talked about how she had to fufill and obligation for her SO’s family because they asked her and she couldn’t back out (clearly referencing the photoshop). She even commented on one of Anna’s posts from the part saying that Anna’s lucky she has it so easy. Now, my family takes a vacation every year in the spring, and Sarah has come with us for the past few years. My parents pay for her like they pay for my other siblings, my SIL, and my nieces and nephews. I just found out from my dad that she called my mom and told her she will only go on the vacation if I’m not there and demanded to be seated in business class. (Usually, everyone sits in business class because while our parents pay for the ticket the rest of us pay for the upgrade- my parents only purchase business class tickets for themselves). My mom said she and my brother could sit in business class if she paid for the upgrade like the rest of us do. My mom also explained to her that she understood that she had a problem with me, but since my parents were paying for the trip they would decide who was coming. Now she’s posting some other crap on the story about how she’s unappreciated and how she’s treated unfairly.
I know I hurt her, and I know it will take more than a phone call and a photo shoot to fix it, but I was prepared to do that. I wish she had come to me instead of staging all of this drama. I’m more shocked she did all of this in a span of a few hours. From the party ending, to me calling and apologizing, to her doing all of this. I think it’s unfair how she’s been acting, especially involving her behavior towards Anna who did nothing towards her. Am I still doing something wrong- because I clearly don’t know when I’m acting like a b*tch or is it actually her fault this time? I know she needs time to recover but I don’t think this was an appropriate way to act.

UPDATE

I messaged my brother, and he agreed she was overreacting a little but explained things from her POV. there has been a rift between my family and her from a while, and I think the issue is no one has tried to bridge it. My brother suggested the three of us meet in a cafe and then he will call the family to arrange a dinner where we can all talk it out, and I can make a public apology to Sarah. I also have reached out to my friends to make sure they are not hurt by the color thing. I didn’t think it would be hurtful, and it wasn’t my intention to hurt anybody, but I’m just going to make sure. Also to clarify since many people have said this this party was a one time thing lol. Last years theme was nautical this year we did colors because I thought it would be cool. The better approach was to have randomly assigned people what color to wear or have had people just pick between white or black. Sarah called me to talk things out, and said she was excited for the photo shoot. The only catch is that she doesn’t want me or Anna to be in it. Anna knows about it but wasn’t planning to come to protect Sarah’s feelings but I feel strange that Sarah would actually say this. While I’m willing to do this for the sake of my family, I don’t want to just be a pushover because I think this is taking things too far. My brother was upset she would make such a demand, but I’m hoping to talk things out at the cafe tomorrow.