40 years imprisonment is too long

I think that woman should have been given a lesser sentence. 40 yrs is excessive. She was first time offender, pleaded guilty without wasting court's time and she did not commit any murder. She would have been given like 10 years. The purpose of incarceration is not just to keep the criminal away from the public, but also to rehabilitate them and reintroduce them to society as better people. She is already in her 30s, 40 yrs will make sure she dies in prison, nothing good there. The courts also have to make sure justice is not influenced by public emotion. What she did is bad, but 40 years ??? Nah