The protagonist is a female FBI??  agent.  I think she is some sort of forensic accountant?  She goes somewhere and accidentally finds a kidnap victim.

She gains a lot of notariety for the kidnapping case.  She and her friend manufacture some sort of evidence to free a man from prison so they can kill him themselves because they think he murdered someone??/

I know this is all very sketchy, but does this sound familiar to anyone?

Not sure if this will help, but I found these references when I searched "mystery forensic accounting" on google.  I'll give you the url too.

A female accountant made her debut in 1993 in the novel Questionable Behavior.³² Teal Stewart, CPA, the lead character, is an engaging intelligent professional who has a man fall dead at her feet. The financial fraud Teal uncovers challenges her professional and personal judgment, and changes her life as she tracks the facts and figures from Cambridge to California in a race with a cunning killer who is trying to kill her also.

In a second novel, A Question of Preference,³³ Teal becomes involved with art and murder as she works herself up the corporate ladder of the accounting firm. A 1995 sequel Unquestioned Loyalty,³⁴ focuses on issues encountered as a partner in a large, international accounting firm.

For another novel about an IRS agent, see Susan Dunlap, Death and Taxes,³⁵ New York: Delacorte Press, 1992. Here an aggressive IRS agent is murdered, and a number of tax concepts are covered. An interesting quote: "He and I are accountants; not mafiosi. Accountants don't think of murder; they worry about double entries."

http://www.bus.lsu.edu/accounting/faculty/lcrumbley/forensic.html

Good luck!

Cele