He asked her if she promised not to tell and she nodded, saying, "Yes." Jack wanted to know for her own information. She was true to promises, she did not lie. Even if it was important to the Order, she would take it as her own responsibilities to bear any repercussions from the secrets rather than reveal them in any manner. Jack was always true.
He opened his eyes and she held his gaze, her emerald eyes betraying the intelligence so many people overlooked. Jack understood things. She might not have been raised in the wizarding world, and she was not a brain surgeon, but she understood the inner workings of the world. If the girl could create her own fireworks, she had to be more than a rash simpleton with a lot of nerve.
He went on a long winded explanation and Jack listened. She could have, at times, reassured him. She, too, had loyalties that lie past the name of the Order. There were some who she would never betray, regardless of their affiliation. She did not stick by the book as far as loyalty to the Order went. But he did not wait for reassurance.
When all was said and done, Jack said, in the quiet of the hospital room, "I've come on my own accord. I came to assist a wounded peer, not for any other motive. I have my questions answered, and now I can assist you through catching you up."
She sat up, thinking. "Grindelwald is gone. Presumed dead. James Roland was accused of aiding him, but Jess and Robert's names came up too. Jess is gone, presumed ill with the same thing you have, but we're not sure. Matt's taken his place in the meantime and..." She smiled grimly. "That's it. We're not the most efficient with our time, you know."