Did a Southern Spy on 16th Street Win Bull Run for the Confederates?

My wife and I spent Saturday morning hiking around Manassas National Battlefield and had lunch in Old Towne Manassas.  In downtown Manassas, I noted that a Civil War Trails sign credits Confederate General P.G.T. Beauregard's July 21, 1861 victory in the Civil War's first major land engagement to Mrs. Rose O'Neal Greenhow of Washington for providing him information  concerning an imminent Union attack.  While there are numerous stories of daring southern belles providing intelligence to grateful Confederate generals, many of these stories seem to be just that, stories that cannot be supported by historical facts.  Can we separate fact from fiction with the story of Rose Greenhow and did the fledgling Confederacy really owe its first victory to this widower in her late 40s?

A social gadfly, Greenhow was a pillar of antebellum Washington befriending both northern and southern movers and shakers including Senator John C. Calhoun, President Buchanan, and even William Seward.   Despite her strong Southern sympathies, she continued to entertain Union officers and Republican politicians at her small home  on the west side of 16th Street across from St. John's Church in an effort to discern any information that she could provide the South  (The approximate site of her home, just across Lafayette Square from the White House, is now occupied by the Hay-Adams Hotel.  Ironically the hotel is partially named after Lincoln's private secretary John Hay who lived on the premises when he later served as Secretary of State.)