Kayla is guilty of not doing something and actively participating!
I will say I'm not convinced Nick wasn't emotionally and physically abusive before the tailspin, though. We have the story of Nick standing over Kayla screaming, from Aaron. People talking about Nick screaming, at the kids. Do you really believe Kayla never got that wrath? The thing with coke is that it can calm one person and hype up another. My ex was one that coke actually made him more tolerable and less abusive. He was an alcoholic, also.
Nick being an attorney could have been his power point. The threats of knowing the law could have been his leverage. We also don't know how Kayla's parents felt. That is the most likely places she would have went. Nick has guns. The deadliest time of domestic violence is when escaping/have escaped. Therefore, her parents or Kayla could have felt that Kayla would bring danger their way. It wouldn't be the first time seeing something like that happened.
Yes, Kayla had options. She still kept her kids in danger. I'm just saying domestic violence is more complex than just leave. Kayla

deserves what is happening.
Kayla has the option to go to rehab and move in with her parents, while CPS case is open. She just wouldn't be allowed alone with the kids until unsupervised is court ordered.