She traveled to Charlotte, N.C., last week for the Democratic National Convention. At a Maryland Democratic party luncheon at that city's Mint Museum, she stood up to be recognized and receive applause.
Rosen edged Chestertown physician John LaFerla in the Democratic primary in April by just 57 of the more than 25,000 votes cast.
She withdrew from the general election in an email to party leaders.
"I have been proud to serve as the Democratic Congressional Candidate of Maryland's 1st Congressional District for the last five months, so it is with great regret, and much sorrow that I must resign," she wrote. "Personal issues have made this the hardest decision that I have had to make."
Harris campaign manager Kathy Szeliga said Rosen's withdrawal "must not delay our troops serving oversees from getting their ballots and exercising their right to vote in such an important presidential election."
Rosen's withdrawal comes during an election season in which Republicans across the country have cited voter fraud to push for new identification requirements at the polls.
Democrats say voter fraud is virtually nonexistent, and describe voter ID laws as a pretext to make it more difficult for the poor, minorities and other traditionally Democratic-leaning groups to vote.
The Maryland Republican Party said Monday it was "happy to see Maryland's Democrats publicly agree that voter fraud is wrong."
"Maryland Attorney General Doug Gansler and Florida Attorney General Pam Bondi should not only investigate but also prosecute Wendy Rosen to the fullest extent of the law," David Ferguson, the executive director of the state party, said in a statement.
Given that the state Democratic Party was "willing to push one of its own candidates out of the race due to voter fraud," Ferguson said, "I'm sure this means they will join us in an effort to purge the rolls across Maryland of illegal immigrants, the deceased, and those otherwise unqualified to vote."
Gov. Martin O'Malley, a Democrat, commended the "swift and decisive action" of Democrats to demand Rosen's withdrawal.
"The action taken today by the Maryland Democratic Party sends a clear message to Marylanders — we will not tolerate any violation of election laws," he said.