Hi there,
I’m am absolutely no expert on g pigs having just rescued 2 last summer however my wee girl got bumblefoot. Her feet are dodgy to begin with due to poor conditions before the rescue centre took ownership of her then after a while I discovered a sore like your pic one day.
Her foot took about 8 to 10 weeks to heal. We started on metacam and one other antibiotic which I cannot remember. Vet x rayed and took swabs and after the swabs came back she changed antibiotics to bayril.
After the meds had finished her sore still looked open and red so we then bandaged it on her advice. We changed the dressing every 2 days for about 7-10 days, I have to say this really helped with the final healing process. She gave us healing gel and popped a bit on before bandaging it its stretchy bandage. It took us a few attempts on many occasions due to wriggly piggy. Think the bandage just kept it protected to allow it to heal completely as obv they’re on them all the time.
Again I am no expert but just wanted to share our experience as it sounds identical.
It will take a long time to heal but I’m sure you will get there x