Carla is not mentioned or seen in Monsters, Inc. It is never revealed whatever happened to her. However, she must have probably been transferred to another scare floor.
Carla has minor appearances in Monsters University. She is seen in a picture used for one of Mike's collectible cards. During Oozma Kappa's "field trip" to Monsters, Inc., Mike and Sulley are excited to spot her. Then, at the end of the movie, when Mike Wazowski and James P. Sullivan are hired in Monsters, Inc., she is seen entering a door at the Scare Floor.
In the Monsters University Fearbook, she is mentioned as an alumni of the Slugma Slugma Kappa sorority.
She is a tall, yellow monster with long, purple claws, which are her big attribute.