A Warm Welcome is the third book in the Anna & Elsa: Sisterhood is the Strongest Magic series.
Olaf has news for Elsa! He has heard of a summer queen from a summer land with summer magic someone with similar powers as Elsa’s, who can control fire and heat. He says her land is trapped in an eternal summer. Olaf thinks it sounds great, but Elsa and Anna think she might be in trouble. Either way, a journey is in order!