Diana Coleman, a longtime Roosevelt community activist who was the lead plaintiff in a lawsuit that challenged Nassau's property tax assessment system as being racially discriminatory in the late 1990s, died on Saturday of pneumonia at the age of 60.

Elected officials and community leaders who worked closely with Coleman say she devoted herself to advocating for Roosevelt's education funding, anti-drug street marches, mentoring youth, assessment reform and other issues.

Her daughter, Sylenia Farris, of Roosevelt, said her mother had been suffering from a cold. "It's just so unbelievable. Her main focus in this world was to make it a better place," said her daughter.

State Comptroller Thomas DiNapoli announced Coleman's death during his inauguration Sunday at Hofstra University, calling the loss "heartbreaking."

"She was in many ways one of the unsung heroes of change and reform here on Long Island," DiNapoli said, citing assessment reform and her leadership in the Nassau Working Families Party.

"If you were in a political battle and Diana was on your side, then you knew you were on the correct side, on the progressive side, trying to make . . . [positive] change for other people," he said.

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"We have lost our fearless warrior," Lisa Tyson, director of the Long Island Progressive Coalition (LIPC), said of Coleman, LIPC's co-chair.

In the 1990s, Coleman was one of six plaintiffs, joined by the federal and state governments, challenging Nassau's assessment system that used a 1938 formula based on construction costs that meant poorer, predominantly minority communities were paying disproportionately high property taxes while more expensive homes in the much wealthier North Shore were being undertaxed.

Two days before the lawsuit was scheduled to go to trial in March, 2000, county officials -- without conceding discrimination -- agreed to conduct a countywide reassessment under court supervision.

Nassau Minority Leader Kevan Abrahams (D-Freeport) said Coleman was a "big proponent of making sure our streets are safe . . . and developing jobs and opportunities."

Coleman served as chairwoman of the Nassau County Board of Health and spent more than two decades serving on the board of directors of the Nassau Economic Opportunity Commission, a Hempstead social services agency. Her most recent role was as the EOC's health administrator.

"She was the people's advocate," said Iris A. Johnson, chief executive of the EOC. "She always stood up for women and the minority community."

In 2009, Coleman helped launch the Long Island Youth Summit, leadership training at Dowling College that draws more than 300 local students.

Nathalia Rogers, an associate professor of sociology and director of the American Communities Institute at Dowling, said Coleman's work was critical to the program's success.

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Other survivors include three sisters, Sylvia Wright of Freeport, June Hardy of Wheatley Heights and Carolyn Grimes of Tampa, Florida; two brothers, Dennis Coleman of Brentwood and Donald Coleman of Hempstead, her twin; and two grandchildren.

Viewing will be from 8 a.m. to 10 a.m. Saturday at Good Shepherd Lutheran Church in Roosevelt, followed by the service. Burial will follow at Greenfield Cemetery.

With Valerie Bauman