Martha Stewart was convicted of lying to the police (Fed).
Do not ever talk to the police. If you have to, have a lawyer present.
Yep. The only reason she's in jail - well, actually two reasons - is her own hubris, and the incompetence of her attorney(assuming of course she didn't go against advice of counsel when speaking to the feds).
She thought she could talk her way out of the situation. Like most people who get convicted after speaking to investigators, she was wrong.