While I agree with you that it is more reasonable that JY or someone changed her clothes over washing them, I contend that it is abundantly more reasonable that no one either changed her clothes nor washed them, but that the amount of blood found on the clothes is consistent with the amount of blood that CY actually got on the clothes. In other words, no one either washed them, replaced them, nor removed her from the home.
In fact, I would argue that it is more likely that CY did not wake up until after the murder took place and the perpetrators left the house.
It seems to me that one theory that has been completely discarded by people in favor of a guilty verdict is the possibility that the child never woke up ... no drugging with adult medication, no child witnessing the murder, no locking the child in the bathroom, no washing and changing clothes, no interpretation of child play by a daycare worker ... just a child that wakes up, goes to her mother's room, sees her mother, and cannot comprehend that she is dead.
Is she carrying the doll that she places with her mother, or does she return to her room to get the doll. The next thing she does is go to the bathroom to get bandaids. Wasn't this in during the 911 call ... "she's gotto booboos" and bandaids? At some point, she stepped in the blood, most likely after she tried to do something with the bandaids.
What happened next? Did she go back to the bathroom? Did she lie down on the floor and think about it? Did she lie on the floor and call for her mom? How did the blood get onto the interior of the bathroom door? Was there blood on towels or a bathmat in the bathroom?
How tall was the child? Wasn't she tall for a 2 year old? What was the height of the bed? Was there something at the end of the bed that she could have climbed on when she crawled into her parent's bed? Michelle was a cheerleader and Jason was photographed balancing the child on one hand. They probably encouraged athletic behaviors like climbing.
At what point did the child wander back to her bedroom and put one shoe on each foot from two different pair of shoes. Adults in the middle of covering up a murder are very conscious of details that will look suspecious. It would almost be instinct to ensure that the shoes matched. I'm of the opinion that only a child could make a dress shoe with a flip flop choice. Why did she put on her shoes? What was she thinking?
At some point she must have realized that there was nothing to be done, which is most likely when she would lie down on her father's side of the bed. She knows that he will there at some point soon enough.
If she slept through the entire murder, the evidence still fits: blood smears on the bedroom door, the doll, the shoes, and where she was found?