Hi Hannah,
That is a strange and challenging case. Prostate conditions are associated with systemic tendencies to thrombosis in people, so it's reasonable to assume the same may be occurring here, implying that the secret to resolving the leg complaint is to resolve the prostate complaint (unless that has already been accomplished). if the prostate issues are still present, I would use a combination of Minor Bupleurum and Ge Xia Zhu Yu Tang to address it. The latter is more anti-inflammatory than SFZYT, which is more suited to a very low grade smouldering inflammatory process, not one that is so fulminant.
If the prostatitis and abdominal effusion issues are 100% resolved, then we just have the DVT to resolve. The infection is just an opportunist. Once we normalize circulation, then the body will resolve it.
We can use severe stasis dermatitis in humans as a model for how to approach this dog, since human patients with that condition have profound lower limb swelling, pitting edema, and non-healing wounds. The best thing I have found for that is Hoxsey-Like Combination, along with a real food diet.
The drugs in use inhibit platelet aggregation, but don't do much for endothelial dysfunction causing exposure of sub-intimal tissues that initiate clotting. Blood movers are called for in that instance, like Modified Xue Fu Zhu Yu Tang. If the infection is nasty-looking and inflamed, consider additionally or instead Xian Fang Huo Ming Yin. These can be used with Hoxsey if you want to hedge your bets.
Hopefully this helps you out. Please let us know how it goes!
Steve