Hillary Rodham Clinton's first step into the 2014 midterm campaign will bring her into the company of family and supporters -- including a loyal backer of her 2008 bid for president who notoriously spurned President Obama and aligned herself with Republican candidates for president.

Former Secretary of State Hillary Rodham Clinton (Photo by Patrick Smith/Getty Images)

Clinton will appear at a May 15 fundraiser for the U.S. House campaign of Marjorie Margolies (D), a former Pennsylvania congresswoman and the mother-in-law of her daughter, Chelsea. The event, Clinton's first political appearance for a 2014 candidate, is being hosted by Lynn Forester de Rothschild, a wealthy former Clinton fundraiser who endorsed John McCain and Jon Huntsman Jr. for president instead of supporting Obama. The event was first reported by Politico and confirmed by a person familiar with Clinton's schedule.

De Rothschild backed Clinton against Obama in their historic and lengthy 2008 Democratic primary battle. In September of that year, she made waves when she announced her support for McCain, the Arizona senator and Republican nominee for president. In an earlier interview with CNN, de Rothschild called Obama "an elitist."

"In an election as important at this, we must choose the candidate who has a proven record of bipartisanship and reforming government, and that's John McCain. We can't afford a president who lacks experience and judgment and has never crossed party lines to work for meaningful reform," she said in a statement at the time announcing her support for McCain. Clinton, who backed Obama after losing to him, expressed disagreement with de Rothschild's decision.

In the 2012 Republican primary, de Rothschild backed Huntsman, a former ambassador, for president. She hosted a fundraiser for the Republican that January. "I don’t really care how this turns out. Well, I care about how this turns out, but I care about supporting the person who will be the best person for America," she said at the time. "I’ve been through that before with Hillary."

Margolies is running for the seat of Rep. Allyson Schwartz (D-Pa.), who is a candidate for governor. She is part of a crowded field of Democrats vying for Schwartz's safely Democratic seat. The district encompasses part of Philadelphia and some surrounding suburbs. The primary is May 20.

The mother of Marc Mezvinsky, Chelsea Clinton's husband, Margolies served one term in the House in the early 1990s. Her legacy was largely defined by casting a tough vote for then-President Bill Clinton's economic plan that hamstrung her bid for reelection.

Bill Clinton appeared at a fundraiser for Margolies last month.