Thanks for the translation!
I think there's more to this than just Emma not wanting to go to the dance with somebody else. Especially considering her mother was carrying around and put to her head a black invitation while praying for Noru to be Emma's knight. Nobody uses black stationary. Other than practical reasons of it being hard to read dark ink on dark stationary it's considered unlucky, terrible news, or a bad omen. Interesting to see why the other guild is showing up to dance, probably as security although why wouldn't the usual security be enough?