It’s a little weird, and I can see being irritated. But I wouldn’t let it ruin a friendship.
It’s not like you had some big emotional investment in the guy already.
I suppose if it was done purposefully (eg. she knew all along she was going to try to be with him, but did it just to mess with you) then I could see being more upset, but it could just be one of those things. (She may not have realized how much she really liked him until it became “more real” that he’d be with someone else.)