Hi Mike,
the image at 12:38:44 with the colour box on it makes me suspicious of an Achilles rupture.
Certainly the Achilles is grossly abnormal,
When I read your text I was favouring a ruptured Bakers cyst that has emptied into the calf, however when I looked art your images I don’t think this explains the fluid deep to the Achilles and certainly the Achilles is damaged.
Like you I prefer one diagnosis to two so I am thinking the Achilles is the problem.
I would like to do a Thompson test and also look at the Achilles in long axis while doors and plantar flexing the ankle looking for paradoxical movement.
If they have had the leg elevated this could explain the proximal migration of the oedema.
Steve