I'm so sorry you're going through this with Josey, but you're in REALLY good hands with Johnny and Callie and everyone else! My dog Jasper was diagnosed with immune mediated pure red cell aplasia (just the red cell series in her bone marrow was affected, like Josey if I remember correctly...) a little over three months ago, and I so feel your pain! A few things I've learned:
--even though IMHA and PRCA are essentially the same (immune-mediated destruction of red blood cells), the location of the destruction (in the veins versus the bone marrow) makes the two super different! I think the initial crash with IMHA is a lot more severe, and the crazy bodily upheaval can cause a lot of systemic problems that complicate the effects of the anemia. The onset of PRCA is slower, and then it's just a whole lot of waiting waiting waiting for the immune system to right itself and let the red cell series build back up again.
--Like Johnny said, reticulocyte counts are a huge deal! It means that the destruction is under control enough and the immature red blood cells are able to make it out of the bone marrow and into her veins without getting snatched up and destroyed.
--With Jasper, and I think PRCA in general, her transfusions did last for about 2 or 3 weeks. Since IMHA-destruction is focused on the RBCs circulating in the veins, putting more blood in circulation, especially when it's not the dog's blood to begin with, can send everything into overdrive and increase the rate of destruction. With PRCA, since the destruction is tucked away in the bone marrow, the transfused blood can kind of sneak in and is able to hold things steady for awhile. Since it can take awhile for the bone marrow to be able to regenerate again, she might need a few transfusions to keep her going until she's making her own, so it's really lucky that we get some mileage out of them!
--It sounds like they're starting off pretty strong in terms of treatment which is so awesome! Immune-mediated lysis can switch targets really quickly, and she's got enough work ahead of her with building her red cell series back up, so getting the destruction under control before it moves onto some other blood component is a big deal.
--Jasper had a really hard time with the herbal milk thistle, but the Denamarin was actually a lifesaver--it's a more bioavailable formula, so she could take a big enough dose to protect her liver and she didn't have any of the gastrointestinal problems that she'd had on the herbal. Keeping Josey eating is the biggest thing, because it's the only way she'll tolerate the drugs, which in turn is the only way she'll beat this, so don't be afraid of the Denamarin if the herbal is a little rough on her!
--BE NEUROTIC! Not to the point where you're driving yourself insane, but IMHA/PRCA is all about staying ahead of the curve. The drugs are really hard on their systems, and the immune-suppression makes every little bug a huge danger, but it helped me to expect the worst and jump on every tiny little weirdness that she came out with, because we ended up catching a lot of issues before they became overwhelming. Check her temp, monitor her stool, and urine dipsticks are really helpful too--a legitimate urine analysis is a good idea to do regularly, but the dipstick can help you get a jump on anything that might be brewing.
--It might be a good idea to check her PCV pretty frequently early on, at least until you have an idea of where she stands and fall into a rhythm. I had Jasper's checked twice, sometimes three times a week when she needed frequent transfusions, and since she started regenerating we've been checking her cbc/chemistry weekly to make sure her red cells are ok, her white cells aren't showing infection, and her organs are holding up against the drugs.
--Ask a ton of questions, do a ton of research, save allll of her bloodwork, and stay positive!! Even when everything is falling apart, don't think about what's going to happen, just focus on putting her back together, loving her, and getting her through it : ) Jasper's 10 years old with an inherited bleeding disorder, and she wows me every day with everything she's managed to work through. Seriously though, I know how overwhelming this is, and throwing myself into researching PRCA helped me keep everything straight, stay ahead of her symptoms, and gave me an outlet for all of the emotional craziness of having a really sick, beloved pet and made me feel less helpless. It's a pretty demanding situation, and having that knowledge can help you be a more effective....middleman, I guess, between Josey and her vet, and your knowledge of Josey and what she's dealing with can help your vet make the best decisions regarding her care. But again, just channel all of that fear and helplessness and frustration into power and ferocity, and get ready to kick some PRCA butt! : )