I only just found out now what's going on with Mia by digging through old threads. I am so sorry you two are dealing with this. Unfortunately I don't have any advice as I have no experience with this specific issue. I myself am an extremely active person, but I have asthma which limits how much I can run and exercise, especially in the heat, so I can relate to atleast Mia in that respect.
Anyway, I know that's not a productive suggestion or answer on what to do to keep the poor girl calm and sane, but just felt I would let you know I feel for you and I'm sending positive vibes your way.