Jaina Katarn was a Jedi healer during the Clone Wars. Upon execution of Order 66 she was in the middle of surgery on a clone commander's heart. The clones who entered to shoot her were told to stand down when she said, "Look, I don't know why you want to kill me, but don't allow this man to die. Let me close him up, then do to me what you will."
She finished the surgery, and was allowed to finish mending the clones waiting for surgery. At some point the commander was woken up. He refused to execute Order 66 upon her completion of surgeries, seeing as Jaina could have easily killed him and it was only because of her that he was alive. So he allowed her to escape. He was later executed.
She ended up on board the Regal Diathim where she found other Jedi. When Kayla, the captain of the vessel, learned that Jaina was a Jedi healer she offered her a position on the crew; Jaina accepted.