Being in vet care is the best place so they can keep flushing out the kidneys and liver, I think your baby will be fine.
Puddles was at the vet for 5 days hooked up to and IV. Back in those days, blood tests were sent out to labs and my vet (best cat vet ever) sent it to a human lab in Calgary (we were in St Albert) so that could be how they were able to narrow it down to a list of items.
I am very surpised the rescue didn't notice that they were not eating
Cat maid to:
Puddles, female Himalayan (16 yrs)
Jasper, male Ragdoll ?? (approx 9 yrs)
Sweet Pea, female silver tabby DSH (approx 7 yrs)
Rose semi feral, a cpietra rescue, female tabby (approx 6 yrs)
Snowball RIP (1991-2005)
In a cat's eye, all things belong to cats.-English Proverb
“While we are free to choose our actions, we are not free to choose the consequences of our actions.” Stephen R. Covey