Nixie is adventurous and fun-loving to the point that she sometimes gets herself in trouble, acting before she thinks. ... However, after the events of the Trident with Zac verses her friends and her, Nixie decides to leave Mako and go back to the Pod again with Lyla and left Sirena, who wanted to stay on land.

Does Lyla come back in Mako Mermaids?

She is the one who at first wanted to get Zac into a human again the most, but on the end she didn't wanted to get him back into a human. She was once a waitress for the Ocean Cafe for one night. She and Nixie will not be returning in season 2.

Why did Nixie and Lyla leave the show?

With Zac remaining a merman despite being in the moon pool during a full moon, it is assumed that she and Nixie gave up on trying to remove his powers. In "The Seventh Cycle", it is revealed by Veridia that she and Nixie left with their original pod in search of a new home.