"What is her temperature now?"
Translation:Какая у неё сейчас температура?
"Теперь" would be used if there was some action before the question and the situation could have changed since, so you'd use it to show some opposition between actions. For example, in this context "теперь" would fit well: "Она болела всю прошлую неделю, но теперь ей лучше" - "She has been ill all last week, but now she feels better". "Сейчас" doesn't have any connotations and can be used in all other situations.