Answer from the White House

So who is the mystery lady? According to the White House the mystery portrait is of Ellen Wilson, the first wife of President Woodrow Wilson who died in 1914. When the photo or the White House tour was filmed, the portrait was on loan, but has since been returned to the Wilson Library or the owner of the portrait.

Mystery Solved!

Mystery Lady in Vermeil Room Portrait

Seven portraits hang in the Vermeil Room located inside the White House. If you conduct a internet search, such as “seven portraits hanging in the Vermeil Room”, you receive the following information. Beginning with the portrait hanging over the mantle and moving clockwise, 1.) Lady Bird Johnson, 2.) Lou Henry Hoover, 3.) Patricia Nixon, 4.) Eleanor Roosevelt, 5.) Nancy Reagan, 6.) Jacqueline Kennedy and 7.) WHO (her name is not given). Mrs. Who’s portrait hangs to the right of Jacqueline Kennedy's portrait in the corner. “Mrs. Who’s” portrait first shows up in photos of the Vermeil Room after 1990, but she’s missing in a photo of the Vermeil Room taken in 2008 (based on photos of the Vermeil Room currently available on-line).
The room houses a collection of gilt silver tableware called Vermeil, a bequest to the White House by Margaret Thompson Biddle in 1956. Could the mystery lady be Ms. Biddle, as the portrait is much smaller than those of the first ladies. Take the tour.

http://www.c360.ca/webring/The_White_House.html