Thinking about Rook and Harding's relationship through the lens of Varric's death like. It's crystal clear it has a big impact on Lace - she's angry and distraught in its aftermath, has to psych herself up just to approach the ritual site ("You need to do it, Lace, it needs to be done"). When Rook suggests that she can use her powers to protect people, the first thing she thinks about is that she could've used them to protect people who mattered to her.
But she sees none of that in Rook. Rook comes across as standoffish at best. "Varric knew the danger." There's no in-game chance to reach out to Harding to share that grief, talk about how it affected them.
But it's not like Rook has to do that, right? Maybe they are not that kind of person. Maybe they grieve, but they don't show it, maybe Harding realises she and Rook just aren't as close as she thought they were, and that kind of stings, but you know. What can she do?
But then things happen in the plot. Weisshaupt happens, Shathann, Cyrian. There are so many chances for Rook to express how sorry they are about someone's passing, the loss of life (and Warden Rook especially does not just observe loss, they experience it and don't have to hide it). Harding sees that Rook can reach out to friends in difficult times. They attend the funeral with Bellara, comfort Taash when they need it. They can grieve, and they can help someone through grieving.
And there's that certain feeling of misunderstanding, maybe a hint of resentment, that Harding, a people pleaser, wouldn't dare to confront. What can she say, even? Why are you mourning all those people and not our common friend? Why not Varric? Why not Varric?
Then, she either dies, never finding out the truth, or finds out the truth so late that the rift between her and Rook has become so big they can't just fill it in. She can't undo the way she had been feeling, feeling about something Rook had no idea about. Tricked by Solas, manipulated to think that Varric was alive. Robbed of the chance to grieve a friend together, time lost forever.
