You have noted in your postings the pain that this is causing you. That sharp stabbing almost breathtaking agony and with as big an area as this is I have no doubt the severity with which you are suffering. IMHO having had chicken pox earlier in life and then receiving the dose of chemotherapy and weakening your immune system the virus became a problem. Only 4% of cases will affect the feet and even then usually only on a single side. That is why I point my finger right at the chemotherapy having reduced your immunity enough this popped up I hope that the doctors have advised you when you are out to keep it covered as much as possible just as this could be spreading to your other leg you also can infect others who could come in contact if they have not had or been inoculated for it. First and foremost though is yourself and keeping you healthy. There is no way to know how much of a hit your immune system took with the dose of chemotherapy but I have seen this far too often and is why so many are reverse isolated in the hospitals to protect individuals receiving it.
IIRC you had mentioned in the time period directly preceding and right after that they had mentioned that your kidney function was reduced. Do you know if that is still the case? It would and can directly contribute to some of the swelling you are seeing in your feet along with swelling from the shingles itself. It will also determine how well your sodium levels can be maintained. Sodium itself is tricky to adjust it has to be done slowly and methodically because as you can tell the damage it does when it gets to low to high a level can also be devastating especially to your cardiovascular system. It is often overlooked in the medical journals as other electrolytes are usually spotlighted when it comes to your heart but sodium does play a key role in it.
Having said that I am glad you are on the anti-viral. I think the hesitation the medical community had in prescribing it to you many days after your first complaints of symptoms was an utter and complete disservice to you. Those medications work best within the first 72 hours.
Holistically there are many things that you can do. That is my goal here with such a lengthy post. I want YOU to have the power to do something. I want you confident and able to know that you are actively fighting against this and put whatever power I can back right where it belongs- In your hands.
Not sure if there is a posting limit here so I will cut this off here and make a separate post for some holistic things for you.