Carla was the lead character in episode 9A of season 4, titled "New Girl on the Block ." According to TVRage , "Reggie makes friends with a new girl named Carla," who was voiced by Alison Inconstanti.
Reggie was curious as to why Carla, a good skater, showed up in town pretty much unnoticed. The gang investigated and found that Carla was living in a homeless shelter. The story dealt with Carla's (initially) suspicious reaction to Reggie's wanting to help her, and how she ultimately became friends with the Rocket crew.