I've got yet a slightly different idea:
-What happened to Caylee may have been done in the backyard on the 16th
-Cayley is place inside the playhouse while Casey gets her things and gets the credit
cards, and any money
-Casey backed the car into the garage to put Caylee in the trunk
-borrowed the neighbor's shovel for two purposes
Used the shovel to turn over the dirt and sand to hide any blood spots or fluid leaks
Used the shovel to break the lock and get a tarp and gas cans to get away
-Possibly hid cleaning rags or something in the shed
-Drove away with Caylee in the trunk and kept her there for several days
-Placed the body somewhere before or on June 27th when the car was
discovered abandoned at Amscot
The timeline to where Casey went on those couple of days, her purchases, and if she drove the vehicle could be a clue to where Caylee is. The excuse of needing a shovel to dig up bamboo shoots is very convenient to cover abnormal dug into dirt areas in the yard.