This is significant because the problem was unsolved for over 300 years and that too using mathematical theorems he had no access to at the time. There are numerous examples akin to this scattered throughout the book that prove her superior intelligence, such as being able to reason out the password that Blomkvist set to the “palm” pda.
Time and again it is shown that she gets stuck on certain things that appeal to her and can't get out of it mentally; stated specifically is the fact that she gets fixated on certain topics and will exhaust all books on the issue until attaining mastery and then never reading them again. As for the most significant criteria, severe social impairment, she differs from the textbook example in the sense that her interactions are impaired because, in a way, she chooses it to be. Lisbeth understands what social norms and customs are from a cognitive standpoint but not from an emotional one, lacking the ability to empathize with others. She gets what the customs are but the why’s don't make sense, so while she is able to imitate a completely normal social interaction, she feels nothing; and usually finds no sense in maintaining the