I run into all sorts of scenarios when I work - this one is out of my league and two Attorneys have given two different answers.

Married couple files first joint returns. Taxes are due and paid.

In sorting through other papers wife discovers rent payments she knew nothing about which were not declared, sales tax on two vehicles (no vehicles were purchased), greatly inflated medical bills.

Her signature is on the Returns but she (and the Accountant) had no knowledge.

One Attorneys says report errors to IRS and beg forgiveness, you can't amend. Other Attorney says do nothing and the Return is audited, pretend you didn't know.

Now - how does she get out from under this (other than divorce which I am sure is coming down the turnpike)?

I would say that it would be much better to come clean before the IRS discovers the mistakes. It's easier to "beg for forgiveness" now than after being audited.
Also look into the "innocent spouse relief":
http://www.irs.gov/publications/p971/ar03.html