I can't answer your question re: specific exercises to compensate for the
loss of muscle in the muscle flap surgery.
It depends on what muscle was used in the right thigh for the surgery and
on whether they took part of the muscle or the whole muscle. Different
muscles in the thigh do different things. Taking them away requires
different compensation.
You don't need all the much muscle strength for standing, but good muscle
control. It's standing up and sitting down where you need muscle strength.
Good luck with your PT. let me know what said.
Simon Kruithof