They were present for Mrs. Clinton’s first devastating political defeat, and they remember it clearly: It was student council president, in their senior year, and a girl had never won.

“I was her campaign manager, so I advised her,” Ms. Ebeling has joked. “Hopefully this one turns out better.”

As a group, the women have been to each of the Bill Clinton inaugurations and the opening of the Clinton library; they were there for her Senate run, when she was sworn in as secretary of state and at plenty of dinners, events and weddings.

When Hillary was first lady, Ms. Ebeling would on occasion meet her at the White House, where Mrs. Clinton would put on a hat and sunglasses, and the two would sneak out for a walk and coffee, undisturbed. They were there during the dark times, too: Monica Lewinsky, the impeachment, the emails.

“My friends are from grade school and high school, and they are incredibly honest with me,” she told The Chicago Tribune in 1996. “There is no evidence whatsoever that they are in awe of me, and sometimes I wish they were.”

The women — a dozen or so in all — plan to travel to New York City on Election Day to support their friend. They campaigned in Iowa in 2008 — on a bus, during a snowstorm, at one point stuck on an icy incline. “There was a moment when we thought we might not make it,” Ms. Moel said. When Mrs. Clinton lost the nomination, she had a pendant engraved for Ms. Ebeling that read: “18 million cracks in the ceiling.”