Yes, the Beastars manga has come to an end. It left fans with a memorable and impactful conclusion that tied up the various storylines and character developments.
She could start by listening. Just being there to let Naruto vent out all the reasons for his hatred. Then, she might share her own wisdom. If she has some sort of special power or knowledge, she could use it to show Naruto that there's more to life than his hatred. For instance, if she can show him different futures or possibilities that don't involve him being consumed by hatred, it could be a start.