Tips on how to use Runaway?

I've fully upgraded her and unlocked all of her skills and my mission is to defeat the act 2 boss using her in my team. Which path is the best for her? Her best skills? Which lair boss is she good against?(I've already learned my lesson with the Librarian).

Before that my go to path was Arsonist to try to maximize her burn DOTs potential since I don't consider her powerful in terms of raw dmg, but I still somehow fuck up with her because she's usually the first one to die in my team(I always put her in rank 2 btw). plz help me git gud with her.