The old lady was WRONG!!!!!!!!!!!!!!!!!!!!!!
LOL... Gotta say you were nicer about it than I would have been. I'd have had to told her to "go get a guard." There is NO general prohibition on photography in any of the Smithsonian buildings.
from the Smithsonian's own website...
Quote: Photography
Still and video photography is permitted for noncommercial use only. Unless otherwise posted, generally, photography is permitted in the permanent collection, but is prohibited in most special, temporary exhibitions. Tripods are not permitted inside the museum building unless permission is granted by the museum's Public Affairs Office. Exceptions may occur in any exhibition or buildings; please inquire at the museum's information desk.
The only exceptions are restrictions on FLASH photography of certain objects which are sensitive to light. You could take a "non-flash" photo of the Gettysburg Address if you wanted to though you might want to explain what you want to do to a guard or docent.
As stated the only other "no-no" is tripods. They WILL let you carry them into most of the buildings, but tell you not to use them. They will not even let you carry them into the National Gallery of Art or the Hirshhorn. You have to check them in the Coat Check area. Once inside though you can take all the photos you like.