She was sent to prison for lying and trying to cover up her insider trading. If she had just admitted and accepted the punishment, it would have been just a financial penalty.

Her blunder was thinking she was too special (or too rich?... she wasn't really that rich) to have to deal with the laws, so she tried to scheme her way around the punishment.

As I recall, her insider trade only made or saved her something like $64k. That's laughably small, and the final punishment to her would have been little more than a slap on the wrist had she not blown it up by lying and cheating to avoid the original punishment.