Nothing wrong with Zagara here, especially towards level 10. In fact, she should rather be applauded. The problem is more with the enemy team, they are apparently totally ignoring her, which is pretty stupid, and that's why she has 0 hero damage. Unless the rest of your team is failing miserably (which you shouldn't given that she provides you with decent exp lead and you are 4 vs 4 all the time because of abathur), Zagara will take it to the core in a matter of moments. She generated twice as much exp as the rest of your team and gives you a decent 1 level lead with heroics, plus, most likely, a noticeable structural advantage. It would be good to have such zagara in your team, she clearly understands her priorities (and hero damage is definitely not one of the especially early in the game), and essentially carries you to the win due to the opps oversight.