Dianne Feinstein, who rose from the San Francisco Board of Supervisors to serve as the city's mayor before spending over three decades in the U.S. Senate, died at age 90, her office confirmed Friday morning.

Feinstein, the longest-serving woman in the U.S. Senate, had been facing calls to resign amid health problems and her advancing age. She died at her Washington, D.C., home on Thursday night, according to a statement from her office.

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Her health declined in public view in recent months as she was wheeled into the Senate for votes and stories about her health and medical expenses circulated in the media. But beyond a statement from her office on her death early Friday, details about her final hours remain scant.

'Worked To Her Dying Day'

However, former California Congresswoman Jane Harman told MSNBC she had a private meeting with Feinstein on Thursday evening at the senator's home in Washington, D.C.

Harman said Feinstein seemed to be in good health but was frail.

"It's a huge, huge loss," Harman, a former Los Angeles house representative, told MSNBC by phone. "I was the lucky one. I saw her at 5 p.m. yesterday at her home. We had a one-hour private meeting. I came by to say hi and to talk about what we could be doing next together, and we did talk about that."

Harman shared a photo of herself with Feinstein that she said the late senator's housekeeper took on Thursday evening.

"I got the hug and the kiss that so many, sadly, on the Senate floor have missed," Harman said. "And there's a beautiful picture that our housekeeper took as I was leaving. But Dianne seemed in good health, frail as she has been for a while."

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Harman said Feinstein was planning to hold some dinners for women in Washington, D.C., and that she would pick up the duty in Feinstein's stead and host the five dinners.

"She obviously literally worked to her dying day to have such an impact on this country," Harman said. "One of the things we've talked about is the impact that she had in the Senate Intelligence Committee as the first woman to chair that committee."

'She Didn’t Feel Well This Morning'

Feinstein had missed some work this week due to health issues.

“She didn’t feel well this morning,” Sen. Dick Durbin said Thursday, noting Feinstein was unable to attend a Senate Judiciary Committee hearing, according to reporting from The Hill. Feinstein had taken part in Senate votes Thursday morning.