Maria
That's between you and your mentor. Contending with first degree murder is serious whether you plead guilty or not.
Understandably she's not happy about that. As much as I don't want you to blame yourself for what happened, I think it was a lapse in more than just ethics there.
There's not enough information available, like what happens if you plead guilty, and what happens if you don't. If you're genuinely sorry you could present a statement. It might lighten the severity of your sentence. But if you're going to say something trite I would advise against that.