Hope your gal is just resting. My smaller (but still 3.5") PZB (E. campestratus) may not make it through molt. He's still on his back after over 24 hours, and hasn't popped the carapace. Not a darned thing I can do to help him. If the carapace was popped, then MAYBE, but at this stage -keep moisture up, keep it quiet around him, and keep my fingers crossed.
Yes, theirs has shed... is still on her back, and is hopefully resting. That doesn't mean that a spider cannot die on it's back post-molt.They said it already shed.