You don't think the nurse actually said that her son ruined the family vacation? Read the original post again, and it's clear that wasn't a quotation. That was the OP projecting. The nurse simply stated out loud the fact that the son was positive, while the OP had apparently wanted to keep it secret (without having told the nurse that).
Honestly, the OP should have warned the kids that this was likely going to happen when they got the consult instead of clear message next to their names, instead of leaving them in the dark. The OP was clearly in denial, hoping that it was all a misunderstanding, and still not wanting to burst the kids' bubbles. As the OP herself says, it was a mistake to take the kids out of school, travel far away, for something that was this much of a risk. Especially without a backup plan & making it crystal clear to them (and herself) that not being able to board the ship was a very real possibility.
It's sad this happened, but not the nurse's fault. Don't shoot the messenger. Sailing right now is a roll of the dice, and
DCL hasn't kept that a secret.