From Wikipedia;
http://en.wikipedia.org/wiki/Ledbetter_v._Goodyear_Tire_&_Rubber_Co.
"Employers cannot be sued under Title VII of the Civil Rights Act of 1964 over race or gender pay discrimination if the claims are based on decisions made by the employer 180 days ago or more."
By the EMPLOYER. Not Ms. Ledbetter.
The employer's decision was to pay her a discriminatory wage. She says that found out about the decision years later when the effect of the negative evaluation was understood.
The ruling was that the 180 statute had expired.
But it would be the same situation had she not even known about the negative evaluation. If I hire Jane at 80% of Joe, who does the same job and has the same qualifications, and Jane only finds out years later, Jane can do nothing about my intentional (even if it were documented!) discrimination.