Usually, such unnatural beings required a sacrifice for them to be summoned, and Maeve was no exception to the rule. She had undoubtedly killed the Salamander King despite its pledge of utmost loyalty to her.
But because of her Fey powers, she was able to reduce the amount of sacrifice needed to call upon her beloved type of unnatural beings, the Valgs.
Besides, the Salamander King was solely seen as a mere pawn in her eyes. Maeve had never really needed him in the first place, and his entire Salamander Family acted as a sort of vacation home for her to fool around while escaping from her actual duties given by Queen Mab, the Queen of Winter Court.
With just one sacrifice, she managed to open the metaphysical realm to call upon the hordes of Valgs as her plaything against the incoming foes. She never knew how Gaeru managed to get reinforcements, much less humans when they were supposed to be extinct or at least turned by her mother's curse.
