If you read the stories you'd see it was someone from the White House who demanded her resignation be sent in immediately over her Blackberry.
If you read the stories, you'll see that it was her immediate supervisor demanded her resignation
saying was because the White House wanted her out. It's clear that the Secretary of Agriculture was keen to get rid of her but that's different from saying that the White House "demanded" her resignation.
I'm not defending the White House here, IMO, the staff there should have been aggressively trying to vet the story before letting anyone take any action. There's a big difference though between using "higher ups" as cover for your own cowardice and actually receiving instructions to fire someone.