I normally do try and leave her and most tanks for last. Problem is I will knock down a toon to red and be ready to finish them off and she pops them back to near full health so I am starting over. Meanwhile I am getting hit by all of her teammates!
I dont mind her in Arena ever since she is near the same level I am. When she and the squad are many levels higher she gets annoying to say the least.
I am still stuck after several retreats. I'll get back at it later, it's bugging me too much now.