The Doctor was already down the hall and in another patient's room and so he did not hear Josh call after him.  

Michelle, raised her head from Josh's shoulder as he stood up.  Then she heard him mention that he was going to change and she might get to see his bum.  Her face went crimson, as she blushed.  She gently released her arms from around him and politely explained, "I'll be outside, so you can change yourself in peace."  She then exited the room, and stood in the hallway looking at the ceiling with her face still red.  

It was an awkward situation for Michelle and she handled it best as she thought she could.