I can't believe how many people are not a fan of Kat and not a fan for the wrong reasons! Is she the best dancer of the rookies? Clearly, not. However, she is very coachable and does not make repetitive mistakes. When they tell her to fix something, she fixes it or shows a real effort in changing it. It's frustrating as a coach to tell someone to change something and they keep doing the EXACT same thing (for example, Courtney's clunky feet), but that is not the case with Kat. She may be a slow learner, but she processes her critiques and changes - exactly what any elite gymnast is trained to do. When she says Judy I will not make that mistake again, she doesn't - and I'm sure that's exactly what they saw. Heck, she even said it in the episode... clearly she has shown Kelly and Judy that when she says it she means it. They wouldn't have kept her if that wasn't the case.
As for her looks or being too skinny... She is a completely fine, gorgeous young woman just like all the other woman on DCC. I can't wait for a day when professional cheerleading is known for its talent instead of "looks". When this happens, maybe it will be respected as such. Which is exactly why I'm happy about Holly, all DCC look standards set aside (again she's a gorgeous young woman), every one of these comments about her are squashed by talent, talent, talent! Which is exactly what should win out everytime.