Here is yet another theory of mine, pulling bits and pieces out of old ones and sprinkling in some new details (discarding old, stale details that did not work, of course).
June 16
George sees KC and Caylee leave just before 1:00PM. Caylee is alive and walking under her own power, IMHO. There are three possible places they go: Kristina's, the elementary school playground, or Lee's. I am guessing Lee's - he's at work.
KC tries to get Caylee to go down for her nap, but she isn't ready. Tony calls and they talk for nearly 15 minutes. After the call KC still can't get Caylee to go to sleep, so she gets frustrated and medicates her with children's cold medicine, maybe Benedryl. KC has been doing this now periodically for nearly a month since Caylee had her cold in mid-May.
Caylee konks out around 1:40, and KC can finally have some peace. She dials up Amy and launches into a 36 minute call with her. They discuss boys, partying, gossip...Amy mentions some stuff on Facebook and MySpace, but KC is not on a computer. KC has to see this stuff, so she throws her stuff back into the car, puts a sleeping Caylee in the car seat, and drives back to the Anthony's - never getting of the phone. They arrive right around 2:00 with George safely gone.
KC grabs a couple things and takes them in, and intends to return immediately for Caylee...but something Amy says causes her to go fire up the computer and start surfing. More gossip, laughs, chit-chat. Call ends around 2:15.
At this point she is into it. She's surfing her friend's Facebook and MySpace pages, catching up on what they are up to, posting on their wall, commenting on photos, checks out the club events for the coming weekend, reads the latest celebrity gossip, maybe even fires up an internet chat with a friend.
Jesse calls around 2:53 and they talk about KC's problems at home, her moving out...a deep conversation that is interrupted by a call from George just after 3:00. He's spoken with Cindy, and they are in agreement: No staying overnight with the nanny. Both she and Caylee need to come home no matter how late KC's event runs.
Caylee...
She's just spent the last hour in the car with temps just above 90 outside. KC unstraps her from the car seat and brings her in, hoping to revive her, but it is already pretty obvious. She's been dead for more than a few minutes. The A/C never really cooled the car off during the short drive over from Lee's, and it did not take long for the car to go above 120 F once it was turned off. KC's mom was right - she's an unfit mother.
KC paces around not knowing what to do. The narcissist inside knows she needs to leave, and with Caylee. She calls Tony and tells him she is free for the evening...can she come over for the night? Tony readily agrees.
KC grabs the laundry bag and puts Caylee in it. She carries this to the car and puts it in the trunk. She packs for herself a couple of items, not really planning ahead beyond the coming eveing. Then she drives up to Tony's.
June 17
KC drives to her parent's home and backs into the garage. She opens the trunk and contemplates what to do next. Nothing really comes to mind. She tries moving the body and notices how stiff it is - no longer a cuddly girl. She is surprised at this and closes the trunk, goes inside to get more clothing for another night at Tony's, and leaves.
June 18
A return trip to the Anthony home, this time with a plan of what to do with Caylee: she will bury her in the yard. Unfortunately, she cannot get into the shed, so like any forward-thinker out there who wants to keep tracks covered, she goes to the neighbor and asks to borrow a shovel. 
She moves the body to the back yard near a possible grave site. Digging even a shallow grave soon proves to be a daunting task, so KC rinses the shovel and returns it to the neighbor. Caylee goes back into the trunk and they return to Tony's. I think she formulated her plan her about using Zenaida "Zanny" the babysitter as a kidnapper. And put the tape on her mouth and across her hair. She added the heart sticker as a kiss... but she also could say that the kidnapper put it there as a signature mark.
June 19
She and Tony plan to meet with Matt C. late in the afternoon to look at an apartment. Prior to that meeting KC is cleaning Tony's apartment and around 3:00PM decides to take the garbage out on her way to Target or someplace like that. She opens the trunk and as she tosses the bag in she notices a stain on the liner under Caylee's laundry bag, and an unpleasant odor. She opens the bag to see where the stain is coming from and sees that fluid has been leaking from Caylee's mouth. Unbeknownst to KC, the movement of the body on the previous day accellerated the process of causing fluids to leak from the body.
This discovery surprises and horrifies Casey. Her first thought is to stop the fluid from coming out of Caylee's mouth. She recalls having Amy's duct tape in her car and pulls the roll out. From past experience she knows she cannot tear it well with her hands, so she runs inside and grabs a kitchen knife from Tony's. She cuts a strip of tape and wraps it around Caylee's head to stop the flow. After doing this she tosses the tape and knife into the car.
Note...I am
not saying pings near JBP indicate she did the taping there. I think this was simple - the parking lot is quiet this time of day. No need to drive out of the way for this.
Note that taping the mouth fixes the decomp date of the stain as 3 days after death. Also note that the bag from Tony's is the one eventually found at the tow yard. KC was so freaked by the fluids that she never went to the dumpster.
June 20
KC knows she needs to get the body out of the trunk, but the bag and trunk liner are soaked. She drives back to the grandparent's and grabs a trash bag, in which she places the laundry bag. On some level she knows this is not "right"...so she gets Caylee's Pooh blankie and puts that in the bag. Maybe a favorite toy horse she has clutched recently is spotted and she grabs that as well. These are put in the bag with Caylee. KC wants to kiss her daughter goodbye, but cannot bring herself to do so. Instead, she places a heart sticker on her cheek or lips, which are covered by duct tape (the warrant does
not say where the tape was).
KC then drives up to Suburban and quickly dumps the body.
