What causes swelling in the pastern / ankle region?
I tend to agree with barefoottrimmer and think this may just be stocking up, which is relieved by moving around more. Have you felt the skin under her hair to see if it is smooth? The reason I ask is that sometimes when mud fever first manifests, there is swelling and tiny bumps that may not be readily visible if the hair is thicker. The bumps develop scabbed over sores. If the skin feels bumpy, that is what I would suspect. If that is the case, I’d cleanse the pasterns well with 0.9% saline solution you can buy at any drugstore, and try to keep her out of the mud. I’d do the cleansing twice a day. When scabs form, gently soak them with the saline and when they soften, gently remove them to expose the skin to air. Cleanse the sores and remove all pus and debris with saline on cotton pads, and use dry pads/gauze to thoroughly dry them. The bacteria are anaerobic and just getting the scabs off and the sores cleansed and dried well usually is enough. The salt in the saline also dehydrates