Penelope Rex and the Problem with Pets by Ryan T. Higgins

Most kids have dogs and cats and fish and guinea pigs. Penelope Rex has Mittens.

Penelope wasn’t sure she even wanted a pet when Mittens came into her life. But now that he’s here, she is determined to make the best of it.
Pets, however—especially ones that are six hundred pounds with six-inch-long teeth—can cause very big, very messy problems.