Fora do Universo
Porque o episódio foi sobre Iris
"I think this episode clearly shows that having Barry's powers for an episode really made [Iris] realize what she's passionate about," Candice Patton told reporters after a screening of the episode. "She understands that Barry having speed is what gets him up in the morning…and I think it reignited for her that she still has to find that, and that journalism is a thing she has kind of put to the side to take up the mantle at STAR labs, but it's still a part of her and it's still the reason that she wakes up."
At the end of the episode, Iris was quick to get Barry's powers back to him, with no real intention of possibly keeping them. Instead, she went back to writing about the Flash, bringing back that journalist side we've all been missing. Executive producer Todd Helbing calls her return to her calling a "reawakening," and said this episode felt like the most organic time to return to Iris doing what she loves.
In-Universe
Porque fazer algo frio não é o mesmo que apagar um fogo ... eles apagam fogo com água ... não gelo.
Independentemente da "ciência", nós vimos no passado que Killer Frost usando suas habilidades tem um preço. Colocar um FIRE TORNADO, mesmo que pudesse, provavelmente mataria Killer Frost.