[1] She was the descendant of men who had been actively involved in the early American republic: Joshua Seney represented Maryland in the Continental Congress and James W. Nicholson was one of the first commodores in the United States Navy.

By the time she was a teenager, the Seney family was living at 4 Montague Terrace in "one of the finest houses in Brooklyn," and her father was the president of the Metropolitan Bank in Manhattan, which was a national institution.

Despite this setback, Mary's father still made major charitable contributions to local institutions such as the Industrial Home for Homeless Children, the Eye and Ear Infirmary, the Long Island Historical Society, and the Brooklyn Library.

In 1908, Mary Sheldon was a forty-five-year-old worldly woman with financial and political experience, when she maneuvered to put Mahler on the Philharmonic's podium and determined to build "the greatest orchestra America has ever heard."

Sheldon had watched her husband, a high-level Republican Party official, help put Charles Evans Hughes in the governor's mansion in Albany in 1906 and Theodore Roosevelt and William Howard Taft in the White House in 1904 and 1908.

Two younger men rounded out the core of Sheldon's group: Henry Lane Eno, at thirty-seven years of age president of the Fifth Avenue Building Co. but far better known in cultural and intellectual circles as a psychologist, poet, and author (his verse play Baglioni was published in 1905); and the European-trained pianist and composer Ernest H. Schelling, age thirty-two, "a connoisseur of books, prints and objects of art", whose wife, Lucy How Draper, had been one of the signatories of the original 1903 plan.

These included wealthy men like John D. Rockefeller, J. Pierpont Morgan, Joseph Pulitzer, August Belmont, Jr., and Thomas Fortune Ryan, but also some formidable women.

Harriet (Mrs. Charles Beatty) Alexander and Mary (Mrs. Edward H.) Harriman, both prominent hostesses and philanthropists in their own right, served as Philharmonic Guarantors and, in spite of Walter Damrosch's comments about rich ladies, also as directors of the Symphony Society (so did Henry Lane Eno).

Their Committee for the two Festival Concerts, which evolved into the Philharmonic Guarantors' Committee, drew up a circular letter in April 1908 that declared: We feel that a man of Mr. Mahler's eminence who has entered so wholly into the spirit of training a really fine orchestra for this City, will have trained the men to such a degree of perfection, that, if in the future, another conductor should have to be considered, this orchestra already formed, shall be of such a standard of excellence as to appeal to other eminent conductors should the moment arise to engage them.

Mr. Mahler sees the promise of the very best in orchestral development in this country and it only rests with us to determine whether we will support the best.Two and a half years later, in November 1910, the Musical Courier confirmed Mary Sheldon's vision.

He then dismissed Sheldon and the nascent Philharmonic Guarantors' Committee with the opinion, "There are people to whom music is only food for nervous excitement and each successive European celebrity visiting this country a toy to play with."

Damrosch was no doubt aggravated to read Sheldon's account of a meeting in May with Richard Arnold, revealing that the thought of a third symphony orchestra in New York had made the Philharmonic Society nervous.

If the story is true, Sheldon must have been delighted at Arnold's capitulation to a plan she and several other wealthy New Yorkers (along with Walter Damrosch) had put forward as early as 1903 and which the orchestra—taking exception to the idea of giving up control of the organization's finances—rejected.

The historic reorganization plan was signed by Mary and George Sheldon, Ruth Dana Draper, Henry Lane Eno, Ernest H. Schelling, and Nelson S. Spencer.