"Maz told me it was Luke's, and before him, his father's." She'd confirmed that with Luke himself-- that is, the Luke who was here-and-now. She'd also learned some more troubling details about the lightsaber from Obi-Wan, but that didn't need explaining yet. Her fingers idly traced over the hilt; visually, it was indistinguishable from the copy of it Luke and Mara had, but she could sense the difference. Yet more to tell when the time was right.
She couldn't help a smile at Finn suggesting Jakku, remembering how he'd reacted when she said she had to return there. He really didn't like it there. She could tell him even more reasons to dislike it, but that was for another time. She'd hoped to put off explaining where they were because that was complicated and she wanted Finn to focus on getting well, but she couldn't just lie or put it off, either. So she considered her words carefully, trying to lead into that explanation while also responding to the remarks about Ren.
"If he does... I'm learning how to really use this, from the Jedi here. Here is... um, there's a lot to take in and explain. But this is a medical ward." That much was, of course, obvious.