Books 4-6 of The Tales of the Frog Princess series.

Book #4: No Place for Magic
When Emma and her beloved frog-turned-prince Eadric travel to Upper Montevista to ask for Eadric's parents' blessing on their marriage, they find his homeland in chaos: Eadric's annoying little brother Bradston has been kidnapped by trolls! Worse, his mother won't let Emma use magic, even to rescue Bradston, and Eadric seems suddenly a bit too fond of the girls from his past. But as they travel through unfriendly lands, battle sea-monsters and vampires, and find allies in unlikely places, Emma just might come to see her Eadric for the strong and loyal young man that he is.
With a dose of bravery and a few clever tricks both magic and not, Princess Emma takes center stage again in this utterly charming and surprising addition to E. D. Baker's fantastic Tales of the Frog Princess.

Book #5: The Salamander Spell
In this prequel to the "Tales of the Frog Princess," Grassina is a young princess-in-training. But as the younger sister to Princess Chartreuse, Grassina is not expected to do much beyond behave herself. When a terrible spell stops her mother from being the good Green Witch, and the Kingdom of Greater Greensward seems to teeter on the brink of terror, Grassina sets off on an errand in the swamp and comes back with some surprises for everyone, including skills that only Chartreuse is supposed to have. Soon it is clear that Grassina has begun to find her own way to the magic she thinks she'll never have, and luckily for Greater Greensward, the audaciousness—and the ability—to save the kingdom itself.

Book #6: The Dragon Princess
With E. D. Baker's trademark humor, wacky animal and human characters, and almost all-new cast, this is the story of Emma's daughter, Millie, who is trying to survive being a magical princess who happens to keep turning into a dragon. When she cannot stop her own magic any other way, she and three friends (one vampire, one troll and her cousin, a young wizard prince) set off for the Frozen North and the Blue Witch. Together the motley group battles fearsome bears, saves imprisoned dragons, and find their way home in style, with Millie having gained control of her dragon magic.