Here is my attempt:
KC got accosted by a bad dude or dudette and was threatened at gunpoint and forced to hand over Caylee as insurance that KC would do the dude or dudettes bidding. (I am sure they can weave some story about what she was being forced to do and why she was accosted). KC agrees to do whatever it was he/she wanted in order to save Caylee. Being a loving mother, KC made sure Caylee had some of her favorite toys.
They made KC duck tape Caylee's mouth (add this only if her fingerprints are found on the tape) so KC lovingly put on a heart shaped sticker over the tape, so that Caylee would be less scared. At some point, Caylee died.
At gun point, they forced KC to put Caylee in the trunk etc etc etc. I am sure the defense team could come up with other details that would fit with the evidence. As a witness to the murder of her little girl, KC was threated that her family would be next if she told.
Fearful that they would now go after the rest of her family, KC remained silent. Her partying was a desperate attempt for KC to convince the bad dude or dudette that she had remained silent as well as a way to deal with and dull her sadness and pain. When Cindy blew the whistle, Casey came up with the various nanny scenarios so that the bad dude/dudette would not hurt her family. Unfortunately, her lies about Zanny made her the prime suspect. The bad dude or dudette have since disappeared off the face of the earth. KC did not know the name of this bad dude/dudette and he/she wore masks. the defense has been following up all leads to find the masked man and strongly believe that the dude/dudette will be found! Regarding the timeline, the original accosting of KC by the maked dude/dudette could have occured June 15 earlier in the day when Caylee was at her great grandfathers. The acutal handover happened the following day
Ok thats my first go - any one want to add or embelish? Please feel free to adjust to better fit the facts....