Dave's ESL Cafe's Student Discussion Forums

[Chan-Seung Lee]

[pugachevV]

I would say that in the absence of any other context, "She is flat out with (or from) work," means she is lying down in a state of exhaustion from working too hard.

On the other hand, if you had said, "She is working flat out," you would mean she is working as fast or as hard as possible.

Another meaning, in informal North American speech, of flat out is, unequivocally.

e.g. He told her flat out he would never marry her.