I liked Nico at the start and even after pushing Will off the roof, which while done in anger, could be seen as self defence because he was threatening her and Dodger's life.
But it just got more and more ridiculous after that, it's not the actor, it's the writing that is the big problem. Even the best actor wouldn't be able to get away with this storyline. It's too much for any character, be even more so for a teen.
It doesn't help that like the GHK they have had Nico kill off characters just so she could add to her kill count. Patrick was dying, they had a MND storyline going, but then decided to have Nico murder him. Trevor was a very popular character and if the actor decided to leave, they should have left the door open or have him die in a more dramatic death, not by the hands of angry Nico.