Alena and her Apis, Gilleo, were heading to Mystery Island for a holiday. Alena put down the carrier with Gilleo inside on the floor, but was knocked over by a Skeith. Then she accidentally picked up a different carrier with a Mallard inside, but didn't realise until she was on the boat. Thankfully, she found a Scorchio on board who had accidentally picked up Gilleo instead of his Mallard, and the two swapped Petpets.
From the picture with the story, it appears that Alena is a green Xweetok. She appeared in issue #24.