As a princess, Glisselda was afforded a privileged childhood. Her governess, Lady Corongi, taught her the history of Goredd, and specifically told her biased information about how Goredd "dominated" dragonkind with their great dracomachia, forcing a surrender. Her teachings were purely theoretical, so Glisselda got little experience in how to actually treat a dragon.
Glisselda also learned from Viridius, the court composer; however, the apprenticeship was a rocky one, and Glisselda consider her and Viridius to be at war. When Viridius decided to find an assistant, one of whose duties would be to teach Glisselda, Glisselda looked over the candidates and decided the only one she would possibly accept was Seraphina Dombegh.
On the day of Seraphina's test, Glisselda arranged it so that the other two candidates would take a trip in a coal chute and get lost in a maze respectively. She spied on the waiting room and overheard that Seraphina's companion, Orma, wanted to go to the Queen's private library, so Glisselda extended him an invitation to lure him out of the room, and in turn lured Seraphina out of the room by having a page boy tell her that Orma was in trouble.
Glisselda waited for Seraphina, setting up a bucket of fish slime up on the top of a door as a prank. Seraphina found her and Glisselda feigned ignorance of Seraphina's identity. They finished setting up the trap, but, now stuck together in the room until someone triggered the trap, they spoke with each other. Glisselda professed to have no interest in music whatsoever, but Seraphina played on Viridius's private harpsicord and likened it to statecraft, pointing out that being too timid or angry with the instrument produced a bad sound. Glisselda observed that any partner would want to be spoken to respectfully.
They had a lesson, and when Viridius finally entered, springing the trap. Glisselda was very amused but reined it in, helping Viridius to his feet. She accepted Seraphina as her music tutor, revealing to Seraphina that this had been her plan all along.
Before a harpsichord lesson with Seraphina, Glisselda chats with her friend and lady-in-waiting, Millie, describing Seraphina as prickly and commenting on Seraphina's poor choice in gowns and hair styles. When Seraphina bursts in, having heard anything, Glisselda is not embarrassed and instead welcomes her in. They discuss Glisselda's upcoming recital during Ardmagar Comonot's visit, and Glisselda tells Seraphina that she wants to play music by Tertius, not by her ex-teacher Viridius.
They practice for an hour before Seraphina's stomach growls, interrupting them. Glisselda giggles that she sounded like a dragon; when Seraphina suggests that dragon humor may be unwise considering the dragon-human tensions and Comonot's upcoming visit, Glisselda says that humans must assert their superiority. She listens as Seraphina corrects her misconceptions about human domination over dragons, using a cockroach metaphor to make Glisselda understand that peace has come not from victory but to prevent mutually assured destruction. Glisselda realizes that the dragons find humans interesting, but may just be waiting for an opportunte moment to strike out humanity once and for all. When she questions how an assistant music mistress knows so much about dragons, Seraphina merely tells her that her father used to read her Comonot's Treaty as a bedtime story, amusing Glisselda greatly.
Sometime that night or the next day, Glisselda discusses this new perspective on dragons to Lucian. At her nightly soiree at the Blue Salon eight days before Comonot's arrival, Glisselda's grandmother comes with several saarantrai and scolds Glisselda—and the room at large—for being so mistrustful and intolerant of dragons. She instructs Glisselda to welcome her guests. Glisselda steels herself and kisses the saarantrai on their cheeks, and then proceeds to ignore them.
At some point Glisselda had made a bet with Millie that Seraphina would not come to her soirees, and this night Glisselda is disproven when Viridius and Seraphina approach her. Glisselda is delighted and calls Lucian over to introduce him to her "dragon advisor." She tactlessly mentions "dragon affairs" within earshot of the saarantrai, but is unaware of her faux pas until Seraphina gently calls her out on it, suggesting that invite the saarantrai to sit or even dance with her. Glisselda is daunted at the idea, but Lucian volunteers to do it, causing Glisselda to tell Seraphina that he's so very good at things because he's a bastard. She is oblivious to his discomfort at this word.
Intelligence lurks beneath Glisselda's ditzy exterior. She dislikes conflict among her friends and strongly urges them to reconcile when they fight, speaking persuasively. Glisselda initially shows a certain lack of social consciousness—which Seraphina observes is Glisselda's right as a princess—but by the end of Seraphina experiences it on the behalf of her friend.
Seraphina describes Glisselda as "breathtakingly mediocre."
Though he is her fiancé, it is a political marriage, and it is not clear whether or not Glisselda actually loves him; however, their relationship is the main reason that Seraphina Dombegh and Lucian cannot be together—Glisselda is not only betrothed to Lucian, but is a close friend of Seraphina, and they do not think it is right to sneak around behind Glisselda's back. Unlike many of Lucian's friends, Glisselda calls him by his first name rather than "Kiggs."
Seraphina is Glisselda's music tutor and later advised her on dragon matters, impressing Glisselda. Glisselda nicknames Seraphina "Phina." Glisselda also finds herself to have fallen in love with Seraphina towards the end of Shadowscale, but decides to let Seraphina and Kiggs love each other in privacy.
Miliphrene is one of Glisselda's favorite ladies-in-waiting. Glisselda herself nicknamed her 'Millie'. She and Glisselda seem to be good friends.