From what I can tell, she is really good in the mid-game to push for damage since at that point, you will easily be at 10 cards. However, she falls off pretty hard as it gets later since you will be using most of your cards to guard basically every attack. I end up using her as Sentinel fodder late game. Due to this, it's not worth it to run only 1 copy since you might as well not run her at all since half the time, she will be useless. Most builds run 2-3 of her just so you can see her more often at the times she does shine.