Has the Vet considered using additional analgesia, Metacam alone, even at the highest dose, is often inadequate in serious GI tract cases. Tramadol may be an option if the Vet would be agreeable. Some Vets would possibly use Vetergesic, but lately there appears to be some talk about it's actual effectiveness in Rabbits and that it is also very sedating. Personally I have always found it useful when it has been prescribed for a Rabbit in my care, but as with all Veterinary Medicine opinions on various treatment protocols change as more knowledge is gained.
Also, including Lactulose alongside aggressive fluid therapy (both oral and SQ or IV) can be helpful. Lactulose is an osmotic laxative and can work well once the Rabbit is well hydrated.
I hope Lily can recover xx