We see her in two entirely different ways!
To me she is a good person who's fallen under a bad influence.
Most everything she had done has been for good, as that is her innate response. However, her desire to know her father, esp being alienated from her mother, led her to pursue unusual avenues. First in the Flash Museum where we
know they haven't gotten everything correct and then to meeting Thrawn. She knows he was one of her father's enemies, but again there are things that she did not know, such as him killing her grandmother.
I think you are correct in that she was naive and Thrawn has taken advantage of that, as we know he can be very manipulative, and she was also obviously angry. He saw the daughter of his greatest enemy, knew she was unaware of several very important things, and had decided to use her for whatever his plans are.
Now yes, she should have told them right from the starts, but then fear comes in. She was in a great place with her parents, actually connected with her mother and teaming up with her hero, her father, in fighting crime. Her greatest dream. Of course she would be terrified of that being taken away and would end up not saying anything.
Sherluc now, was an
ass! He was so into his 'big moment,' playing up to his audience, that he didn't see or care that he was doing something that she should have been given the time to do. He should have told her he knew, and then gave her the time to come clean with her parents. Instead, he forced a situation that put her and her father at odds.