In truth, Mara liked having this family unit. River may not be hers and Luke's biologically, but it didn't take blood to make a family. All one needed was the capacity to love and be connected with others. And the fact that this little family unit came without having Jedi family drama tacked onto it and beyond refreshing. Luke might take offense if he knew that, but Mara would stand by it. Of course, it was worse here than it had been in their own universe because of everyone being from different points in time. There was so much tension between them all, and it seemed that when they tried to come together as an actual family, something would happen to break them apart again.
So she was incredibly grateful that Luke was here, that River was here. It gave her relief from her mixed feelings on Jacen, which were now tilted far more in the direction of being hate currently. Mara did need that balance to keep her from killing Jacen, which is what she currently wanted to do. But that wouldn't solve anything, save to quench the thirst for vengeance that Mara had. And oh, it was there, she just kept it to herself. She had managed to keep it hidden, especially after Jacen had saved her life after Pestilence had been disposed of. But now it was trying to come to the surface, and so she tried to do what she could to keep it from getting to that point.
As Mara listened to the explanation of why the documentary was wrong, she surprisingly followed along. After all, Mara was a pilot, among about a thousand other things, but she'd flown many different kinds of ships in her time. So really, she could see River's explanation. Of course, without the girl pointing it out, Mara wouldn't have seen it.
"It sounds like they could've used a mechanic from Coruscant that knew how to properly build aircraft." And that was Mara's simple response. "Now that you mentioned it, it's a wonder that the Hindenburg ever got airborne to begin with."