So, I (24F) recently bought a gorgeous fitted dress that I've been saving up for months, it's tailored for my measurements and is in the style of a lady-in-waiting dress from the early 1530s. It's a beautiful piece made specifically for a renfaire that I’m attending soon, I spent 2.5K on it plus all the accessories. I've been looking forward to this event for ages and planned to wear this dress for the event.
Enter my SIL, "Emma" (29F). Emma and I have always had a somewhat strained relationship. She tends to be a bit demanding and has always had a sense of entitlement, but I've tried to keep the peace for the sake of my brother and family harmony.
A few days ago, Emma came over for dinner, saw the dress hanging in my room when she went to the bathroom, my door was open, and immediately fell in love with it. Emma is quite a bit taller and heavier than I am (4'11 and 110 to 5'9 and 200, so the dress wouldn't fit her properly without significant alterations. She asked if she could borrow it for a party she's attending next weekend because the theme is historical figures, and she planned to go as Anne Boleyn. I politely declined, explaining that I had saved up for it and was planning to wear it to my own event and that the dress was more of a lady-in-waiting dress than a queen's dress.
Emma didn't take this well. She started insisting that she needed it more than I did, that she had nothing else to wear, and that it would be selfish of me not to let her borrow it because I have other dresses I can wear. I do own other dresses I have worn to reinfaires before, but this is the first time I've had enough money to get a custom-made dress instead of sewing it myself out of thrifted items.
I stood my ground, saying that while I understood her situation, I wasn't comfortable lending out something so expensive and personal, especially since it wouldn’t even fit her correctly.
Things escalated quickly. Emma got upset and accused me of being selfish and inconsiderate, even saying I was calling her fat because I didn't think it would fit. My brother tried to mediate but ended up siding with Emma, saying that it wouldn't hurt to lend it just this once and she could make it work. This made me even more upset, and I might have said some things in the heat of the moment that I now regret: that even the tightest corset wouldn't let her fit into my dress and that even if the waist, hip and bust did fit that she would be dressed more like a prostitute of the era because her calves would be visible. I also told her it was likely she would tear or rip the fabric while trying to wear it.
In the end I told Emma that she was acting entitled and that just because she wanted something didn't mean she automatically deserved it. Emma stormed out crying, and now my brother is mad at me too. My parents think I should have just lent her the dress to keep the peace, but I feel like I have the right to set boundaries and not be pressured into giving up something important to me, especially something that would likely be damaged or altered significantly. Even if it was just a dress. AITA?