From the Super Mario Wiki
Mrs. President was the First Lady of the United States during The Adventures of Super Mario Bros. 3, and is the wife of Mr. President. An animated version of her appeared in the episode "Reptiles in the Rose Garden", and was earlier mentioned by Sgt. Slaughter when he spoke to the President in The Super Mario Bros. Super Show! live-action segment "Caught in a Draft". Though never called as such, Mrs. President is obviously based upon Barbara Bush, the wife of George H. W. Bush, who was the President of the United States around the time The Adventures of Super Mario Bros. 3 originally aired.
In "Reptiles in the Rose Garden", King Koopa used a Levitation Beam to warp the White House, along with everyone inside (including Mrs. President and her husband) to Dark Land. Shortly afterwards, Bowser banished the White House to the bottom of the Mushroom Sea. Mrs. President feared for their lives, while Mr. President simply continued his phone conversation.
When Mario showed up wearing a Frog Suit, Mrs. President was frightened of him at first. However, Mario quickly proved himself to Mrs. President by flushing the water out of the partially-flooded White House, allowing it to rise to the surface of the Mushroom Sea. As a thank you, Mrs. President told Mario that she and her husband would refer their friends to the Mario Brothers Plumbing.
When Mario managed to warp the White House back to Washington, D.C., he accidentally placed it on top of the Washington Monument. Mrs. President told Mario that her husband couldn't run the country like this. Although she was never seen again on the show, it's assumed that her life returned to normal once the White House was returned to its proper spot.