The May 15 fund-raiser will be held miles from the district, at the Upper East Side home of Lynn Forester de Rothschild, chief executive of the E.L. Rothschild investment company and a longtime backer of Hillary Clinton.
Rothschild is a British baroness who has often supported Democratic candidates, but in 2008 backed Republican John S. McCain, saying she believed Barack Obama and other Democrats had steered the party too far left.
The invitation for the event suggests contributions of $1,000, $2,600, and $5,000.
Larry Ceisler, a Philadelphia political and public relations consultant, said that the event might raise some cash, but that he was unsure how much it would affect voters.
"The real question is, are we going to see Hillary Clinton in any kind of advertising?" he asked. "Are we going to see her on a mailing, or hear her on a robocall doing her part to persuade voters? That's where she really makes a difference."
Margolies, who held the 13th District seat from 1993 through 1995, has been viewed as the front-runner in the May 20 election, given her name recognition and support from the Clintons. But she has struggled to match two of her opponents, State Sen. Daylin Leach and Valerie Arkoosh, in fund-raising.
Aren Platt, a senior adviser to Leach's campaign, said he was surprised Hillary Clinton was not planning to stop in Philadelphia.
Ken Smukler, senior adviser to Margolies, said the event was taking place in New York because after the recent campaign appearance by Bill Clinton, some local donors may be tapped out.