My answer has to do with the personality of most people who take up such skills. Introverts.
Introverts, tend to score higher on IQ test, because their personality is a better fit for thinking and abstract problems. They actually enjoy these types of activities. It makes them feel good. It motivates them. She seams to be a classic introvert type personality, as do most hacker characters in movies. Speaking for my self, I know that I can spend 20 hours a day learning about how different things work.
As far as how easy it is to hack stuff, well it depends on how well you have prepared/practiced. What you see in the movie is a person, you don't see the 3 years she might have spent writing programs, building networks and testing her skills. It seams to me like she was not really working before the movie and did what ever she liked. She might have 10 years experience in cracking systems. She might not be actually cracking the system in the movie mearly gaining access through a back door she spent 6 months putting in place.
If you want to understand how easy it can be to gain access, their are software tools that you can download for free right now. That have sets of attacks pre-loaded to crack certain types of software. Even a moderately knowledgeable person would be able to figure out how to use this software. A highly motivated person could do quite alot with it.
The weakness in most security systems is the people who use them. If you know them well enough it is quite easy to gain access.