Why do women get out of criminal charges easier than men?

Why did the system let a woman (Mary Winkler) off for murdering her husband for psychological abuse. She serves only the time she waited for her trial and only had to stay in a mental hospital for a few months. Shes completely free now and gets raise her kids. Someone who commits involuntary manslaughter kills someone can get 5-15 years. She commits cide and is free as a bird. Why does the law fail at delivering justice sometimes?