A simple detail that the defense will hope that the jury won't believe. Most people find it hard to believe that a family doesn't notice a pregnancy.
But I thought of another theory....
JB says he will explain why KC didn't look for Caylee. Why wouldn't she look for her missing daughter? Because she thought CA had found Caylee and taken her home with her! Because she thought CA had wanted to make her worry about Caylee.
How about KC left Caylee in her car while she ran in somewhere for a few minutes. When she returned to the car Caylee was gone and she thought she saw CA's vehicle turning the corner. She tried to call CA and got no answer. She looked at CA's myspace and saw the entry about her missing Caylee and that made her mad. She figured CA saw Caylee in the car, figured she would be in trouble for leaving her in the car, figured CA wanted to make KC worry, she thought Caylee was in safe hands with her mother, so she partied. She thought that Caylee was with her mother and she was in trouble, she was already mad so she didn't know Caylee was missing until her mother called police. She thought CA was bluffing. Now she wonders if CA may have harmed Caylee. After all, CA allegedly slapped KC. The expartee may be an attempt to obtain the psych records on CA.