CHICAGO (CBS) — It’s Chicago’s oldest hospital, treating patients since before the Civil War, but Mercy Hospital wouldn’t be here today without the spunk, smarts, and determination of a 77-year-old nun.

Now, its CEO, Sister Sheila Lyne, is retiring. She looked back on a lifetime of service with CBS 2’s Derrick Blakley

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Walk the halls of Mercy Hospital with Sister Shelia Lyne and you’ll see gratitude for a lifetime of dedication.

When she became CEO in 1976, Mercy was in critical condition as there were too many poor patients who didn’t have insurance. Sister Sheila’s savvy kept it open.

“The one thing I can remember is I was almost in tears thinking we weren’t going to make it,” said Sister Sheila.

Then, she left to work for Mayor Daley as health commissioner, but she returned in 2000 when Mercy was losing $40 million a year.

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Sister Sheila got help from the feds and built up hospital’s cancer and cardiac care with star doctors like Paul Jones.

“She is a true icon and has done phenomenal things for health care in Chicago and certainly on the South Side of Chicago,” said Dr. Jones, a cardiologist at Mercy Hospital.

Now, she plans to take medical care to the poor, literally going door to door, to track down needy patients.

“We’ve got to begin to find the patients that don’t know what they need to do,” said Sister Sheila.

Through the hardships at Mercy, Sister Shelia carried a bit of old-fashioned Chicago clout.

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All of Richard J. Daley’s children were born there, including Richard M. Daley. And as Sister Sheila told CBS 2’s Derrick Blakley, even when the Daleys chose to get their health care elsewhere, they never forgot where they came from.