Update:
Posie managed to eat the equivalent of a full meal over 4 hours today (oh, yesterday) and kept it all down. She was also back to her normal bouncy self.
A slight issue arose at 3.30am when she wanted out. She was out there for a few minutes and when she came in there was definitely something not right ut she ran past me with her tail between her legs. When I got to the bedroom she was sitting on a pillow looking very sheepish. Then I noticed the poo on the carpet, in a trail as if she'd dragged her bum. Then I noticed the big chunk of it stuck to her tail...and the pillow.
She clearly knew it was wrong, but it wasn't her fault and after the time sheshadnlately she was never in fear of being told off. The hard part was getting her to get off the bed and into the bathroom for a impromptu shower.
A change of bedding and bit of carpet cleaning later and were ready for bed again. Unfortunately now I can't get to sleep.

The good thing is that I know for certain that she is processing food all the way through her system rather than just throwing it up. Hidden blessings, eh?