Thankfully, Percy has been expecting that kind of reaction, and reacts accordingly.

"He seriously just came up to me and asked! He had clothes too which was kind of weird but - the fish, Annabeth."

Percy sets down his glass and retrieves the dress he'd gotten her with Vanessa. He'd made sure it was in her favourite colour and that she'd be able to strap a knife under it somewhere, but other than that he'd just had to trust their friend with the details. He hands it over, trying to cover his continuing nervousness with an eyeroll. "Atlanteans, seriously. This is what happens when you make friends with a king, I guess."