I recently watched Elevator to the Gallows and wow, what a spectacular movie!

I was left with a question at the end:

The police tell the main female character that she will do more prison time because she encouraged the murder. It doesn't make any sense that her punishment would be more severe than that of the man who actually shot and killed his boss and set it up to look like a suicide. What gives?

And furthermore, it would be very difficult to prove she encouraged the murder. Sure, they were having an affair, but what evidence do they have that she asked the guy to kill her husband?