For example, if Karen hadn't lied to Ben to get him to the nursing home to talk to Fisk's mother, Fisk might not have killed him. His reason for killing him was that he went after his mother. He didn't. Karen did.

That's not the same as her being responsible for Ben's death, though. Like, did she even have reason to believe that Ben would be killed because of that? She didn't know the depths of Fisk's instability and thirst for vengeance when she decided to trick Ben. It's entirely possible she thought they were going to find the smoking gun, that Fisk wouldn't be able to touch them once they talked to his mom, that Ben would immediately print the story and Fisk would be in too deep shit to do anything about it.

I think Karen was naive, but she never had reason to believe that the corrupt businessman she was going after was actually a supervillain who would murder a man with his bare hands. If she knew how dangerous Fisk was, I would call her partially responsible (because Fisk is ultimately the one responsible for Ben's death), but I really don't think she can be blamed for getting Ben killed when she had no idea that it would happen.