Anyone have any papers on it?

I'm currently in a project that has been going on for over a year now. We did a ton of requirements gathering, made design documents, did paper prototyping, had signoff on the design and everything.

So away we went on coding. Now, about a month before it goes live, our graphic designer/usability specialist is demanding we do another round of usability testing. We all agree it would be a good idea, but we told her that she did her testing before/during the design being built, and that any usability changes will not come until at least 6 months after the project has gone live.

This seems to have blown her mind, she is basically demanding that we do this testing and hold off and release the project a month or two later. We told her that she already did her usability testing and so the product is usable and any changes people find, we will make for the next version release.

Has anyone done any research into this that could list some papers either proving our point (the developers) or the designers point? We all agree that extra testing should be done, but we also think it is ridiculous to hold off another 2 months when she already spent months getting this design finalized in the first place.

What say you VBF?