I know that what Shannon Smith said is highly offensive and upsetting, but do please keep in mind that the US legal system is adversarial in its nature. It is not a system in which counsel are working together to find a unified truth. Her job is to defend her client zealously to the best of her abilities within the rules of the system. No matter what a person is accused of having done, that person is entitled to principled, committed advocacy.
When a lawyer spends a long time on a complex case with a client, working her/his best to represent that client zealously, it's quite common for that lawyer to become personally and emotionally invested in the client's side and story. That's part of what can make a lawyer a really good advocate.
I have nothing but respect for people who choose to take on the difficult work of ensuring that individuals accused of shocking, offensive, and terrible things have their constitutional rights.
I am not sure this is the most effective way for her to advocate for her client. Given the weight of the evidence against him, the massive public disgust, and the fact that he's chosen to plead guilty (however grudgingly), her client would probably have a better outcome if she advised him to show some remorse and get the sentencing over with quietly without sending any more letters to judges. Sure, discrediting the alleged victim is a common defense tactic in sexual assault cases, but this is not exactly an ordinary case.