Jaina wasn't about to disagree with him, regarding the Dark Side. She was up to her neck in it back home, and knew firsthand the sort of pain it caused. She was also dealing with it here, as well, in the forms of her grandfather, her own twin and, of course, Exar Kun. Not to mention her own brief stint with the Dark Side following her younger brother's death.
However, these were all things she wasn't quite comfortable discussing with a veritable stranger at the moment. So she opted to remain silent and instead let him speak again before replying.
"I know I'm right, but I'm sure you'll see for yourself." It wasn't said with disrespect, but rather a simple statement of fact. She didn't expect him to just take her word for it, and would be extremely surprised (and a little disappointed) if he did.
There was a slight hesitation before Jaina spoke again, as she tried to figure out how to delicately explain the next bit. "Also, you should probably know if you don't already... apparently we're all fictional, here. The most recent holo that the people of this planet are viewing is, in fact, about Anakin Skywalker's fall to the Dark Side." It was clear from her tone that she didn't like this information, not one little bit, but Jaina also knew there was no escaping it. Obi-Wan deserved to know it, and come to terms with it however he saw fit.