I'm so sorry about Gucci's anemia. Have you received the biopsy results yet?
What units is the RBC count given in? I'm a bit confused, because in US measurements (M/μL), 11.5 or 13 would be a very good number; it wouldn't get critical until it was about 5 or 6. Do you know the numbers for HCT (or PCV), HGB, and reticulocyte count?
I guess the blood chemistry didn't show any abnormalities? My kitty was anemic as well, but she had chronic kidney disease. With CKD anemia is almost always non-regenerative, and when HCT drops below 20, an erythropoietin stimulating agent (ESA) is given by injection, along with iron. Gucci is young, though, so I wouldn't think CKD is likely, and I don't know whether the anemia is regenerative or non-regenerative. You could ask the vet about this, although I imagine that an IM specialist would have mentioned ESAs if they were an option.
The other thing I can think of that would cause anemia is internal blood loss, like a GI bleed (it's less scary than it sounds).
I'm not at all familiar with interferon syrup, but I believe that prednisolone is only effective for stimulating RBC growth if the anemia is due to something with the immune system.
To try to bring up the HCT, you could try feeding chicken hearts and/or chicken liver (most kitties love liver), and asking the vet for a vitamin B12 injection. You can also give B12 orally. But if Gucci's anemia was severe enough to require a transfusion, I don't know how much difference these things will make in just a week.
I have my fingers crossed that Gucci's body starts making more RBCs very soon!