I havent really been paying that much attention but it seem like she is fucked. Was there really a huhe gap of time between when her child went missing and when she called the police?
about a month, to which Casey(the accused) went partying, drinking, and got a tatto reading "The Beautiful Life". during this time Casey constantly lied about where her daughter was until her parents got fed up with it and she confessed that the girl had gone missing.
to answer the OP's question, when the area where the body was found was searched by dogs it was under water due to rains (the whole area was a swamp). water is very good at hiding scents from dogs.
alot of the evedince is circumstantial, which makes a conviction hard. Yet i have a feeling she is guilty of something. the massive web of lies, including trying to pin sexual abuse on her father, makes me think she is hiding something. it could have been a death attributed to child abuse, since there was duct tape on the victims mouth and nose, possibly to shut her up so her mom could party. that i belive would be considered an accident, but still she could be charged with child abuse and possibly manslaughter. but it coiuld still be murder if she was that desperate to get back into her party/ romancing life. or there is always the defense, which is the girl drowned in a pool, Casey's father hid the body, and Casey only partied to hide emotional distress caused by sexual abuse by her father.
i personally think that, one way or another, she is responsible for the child's death. she has lied so much it goes beyond "being scared". i dont think the death penalty(one her possible punishments) will be sentenced, but i think she may be convicted.