The reason she was arrested is because it is considered bank fraud.
If you use your credit card, and you don't pay it off, then it's a civil issue of you defaulting on a loan.
If you write a check, and you don't have the funds to process it (overdraft), then you've committed bank fraud. Often, the bank as a courtesy pays your check anyway, and you end up in overdraft. And often you didn't intentionally mean to write a bad check, so there is no intent (remember: a crime = action + intent). When you write $3M in checks when you know your account balance is around $20, you know darn well you are writing bad checks, even if the bank foolishly continues to provide overdraft coverage.
That's probably why she was arrested.