AITAH for telling my sister she can't use my wedding date because she's "calling dibs" on it?

I (27F) have been engaged for 3 months. My fiancé (29M) and I picked a date for our wedding October 15, 2025. We already put a deposit down on the venue and sent out save-the-dates.

my older sister (30F) got engaged last week. She called me yesterday and said she and her fiancé want to get married on October 15, 2025. She said she "called dibs" on that date because it's their anniversary.

I told her that's literally my wedding date. I already paid for it. she said I can just change mine because she "called it first" even though she wasn't even engaged when I picked it.

I said no. I'm not changing my wedding date. She got upset and said I'm being selfish and ruining her "vision" and that I can get married any other weekend.

Our mom called and said I should just move my date to "keep the peace" since I have more time to plan anyway.

AITAH?