Queen Hylda is the queen of the goblins, living in Gildingham and is introduced in the book 5, Lodestar, though she is mentioned multiple times before.
When it's announced that Sophie will attend the Peace Summit, Queen Hylda requests to meet with her regarding the Summit. She gives Sophie a list of things that she wants Sophie to support her on, this includes things such as "She wants the ogres to turn over all their weapons and agree to stop any sort of offensive or defensive training, wants them to surrender the borderlands they share with the goblins, and wants King Dimitar to turn over the ogre that killed Brielle."
Other than this, the only thing that is shown with Queen Hylda is that she says that Fintan should be allowed into the Peace Summit to stand for the Neverseen.
Queen Hylda has a giant snake named Twinkle that can move at supersonic speeds and pulls her carriage.