There's a reason scales are used to symbolize justice. While I agree with your point that the sentence is lenient for the use of deadly force, it is likely that prosecutors realized that this woman's background and profile suggest she poses little future risk to the general public. 

If I were the judge and did not have to adhere to sentencing guidelines, I would sentence such a defendant to 20 years, with 18 of them suspended on the condition that she never reoffend. And to your other point, yes, I would revoke her driving privileges for life. She might never again aim a car at someone in a fit of rage but that's a risk I would not take.