Although this article is based on canonical information, the actual name of this subject is pure conjecture.
A Sick Deadly Nadder appears briefly in the game, School of Dragons in the player Quest, "What a Mess".
This unnamed Deadly Nadder became ill after drinking dirty water.
"Astrid was walking on the school grounds when she spotted a sleeping dragon on the shores of the school lake. The dragon didn’t look too well, and the dragon trainer immediately knew something was wrong. It didn’t take long for her to realized the water the dragon had been drinking was filled with dirt and debris."
"A Deadly Nadder drank from it [pond] and now she's so feverish she couldn't even smell my hand. I think the water might be tainted."
―Astrid in School of Dragons
Astrid finds this Nadder unwell next to the lake at the School and seeks out Hiccup to formulate a way to help. Hiccup devises a Water Filter and after offering the Deadly Nadder clean water, she starts to feel better again.
This unnamed sick Deadly Nadder is mostly black with a yellow underbelly and pink-hued spines. Despite being a resident "wild" dragon, she has blue and yellow racing paint on her body.