Guinevere is first mentioned by Professor Barnabas Greenbloom while he, Firedrake, Ben, Sorrel, and Twigleg are eating mushroom soup in the basilisk cave. Guinevere is said to be about Ben's age. She is first seen on a boat heading for the monastary. She looks at the river below and sees a massive golden dragon with a soggy dwarf clinging to one of its horns. She tugs on her father's arm and points, saying she saw Nettlebrand, but by then he had sunk into the water so he couldn't be seen. Professer Greenbloom shakes his head, saying she was being silly, and Guinevere insists she did, descibing him in detail to prove it. Her dad says that is was possible, then promises they will warn Firedrake and the others when they reach the monastary.
Ben is said to blush slightly when he is said to be about her age and when he meets Guinevere. After a while they are inseperable and best friends. He is much beloved to the Greenblooms.
Guinevere is very close to her father. She belives in fantastic creature just as much as her father does, and sometimes comes with him on his searches for them.