Just to summarise our phone conversation:
1. Please put Miru on a bland diet (my personal choice would be Hills i/d - dry). Min 6 weeks course
2. Take her back at your local vets and ask for a gastro-intestinal work-up
- bloods: haematology, biochemestry, electrolites, FIV, FeLV, FIP;
- special intestinal bloods? Foalate, TLI, Cobalamine
- extended faecal screen: parasites, protozoars, viruses?)
- imaging: abdominal ultrasound, colonoscopy +/- biopsy.
All this can be done in the following few months if Miru is stable on bland diet (Hills i/d?). Please also ask your local vet if they'd do a Direct Claim with Pet Plan so that finances wouldn't be a concern at this stage.
If any deterioration, we should consider hospitalising her. Also, please make sure you keep her indoors as much as you can so that we avoid a pregnancy (her being underweight would impose a high risk on kittens).