I believe that when she originally disposed of Caylee, the remains stunk. KC expected somebody else to find Caylee, while KC was "away" doing who knows what, and CA or LE would have to "break the news to her"---all those calls "Where is Caylee?" "Oh, she's at Disney World with Zanny."--"No, you'd better come home. We've found her body in the woods" "Oh No! It can't be! I just spoke to them yesterday and everything was fine!"--see where I'm going?? It never crossed her mind that cell records and pings would track her moves. She'd already been researching the sim card/lost numbers bit. She had it all worked out...but nobody found the baby....
She didn't call LE because the imaginary babysitter would vanish AFTER Caylee was found. Until then, everyone was on a happy vacatuion and the whole scene would come as a huge shock to KC. Friends would rally to support her, mom and dad would comfort her, just like in the movies...