Fireworm (Dragon)

You maybe have been looking Fireworm (Riders of Berk)

Fireworm, the only female Monstrous Nightmare in the book, is the bright red, stubborn, and tenacious dragon of Snotface Snotlout.

In the Book
Snotlout captured a Monstrous Nightmare and named her Fireworm. She is reasonably brave in the book; for instance, as she leads the Green Death to the Purple Death so that they would kill each other. She also loves to sneer about stuff she hates.

In the Film
Fireworm makes no apperance in the film; however, a Monstrous Nightmare named Hookfang is trained by Snotlout. Unlike his Fireworm, Hookfang is male and has a very different personality.