Hi Mike,
I agree that BZYQT is worth a try here, given its ability to stimulate the immune system, bone marrow, and protein synthesis (via Bupleurum's effects on mRNA transcription in the liver, with subsequent increases in albumin).
I've been looking at parvo in light of the Shang Han Lun (Treatise on Cold Febrile Disease). It appears to be a Shao Yin (Lesser Yin). Shao Yin organs are ones where Yin and Yang comingle in almost a perfect balance, namely the Heart and Kidney. If that balance is upset, the patient can experience Yang deficiency or Yin deficiency. The former produces signs of severe cold and 'wetness', the latter signs of heat and dryness. I think parvo is, naturally, of the former type.
So technically, we need a Shao Yin formula that fits your patient's presentation and has the desired biomedical effects. A strong option is a formula called Zhen Wu Tang (True Warrior Decoction), which is a major Shao Yin formula for edema. I don't know it has the desired biomedical effects on albumin, however.
The basic Shao Yin formulas were simple Yang warming, Damp draining formulas centered around Ginseng (an imbalance of Yin and Yang damages Source Qi, which Ginseng rescues). Ginseng does promote albumin synthesis, according to a Japanese study in 1972. It also promotes, at least in humans, the proliferation of erythrocyte progenitor cell lines in the bone marrow. So there's a biomedical basis for effect there. The formulas include Fu Zi Tang and Fu Zi Li Zhong Qan, as well as Li Zhong Tang itself.
So there are some ideas for you. You could add Ginseng to Zhen Wu Tang, or use two Shao Yin formulas. You'll need to make or specially order those, however, so in the interim, try the BZYQT.
Good luck!
Steve