I play her all the time. Awesome at defense, like others have said. I've def been a noticeable factor in winning games on defense and she can be super fun if you have enough time to setup your turrets well.
Make sure shields are always up on everyone (pretty easy) and put the turrets up above players (to help avoid dying from regular gunfire). I like to use upper corners in smaller buildings or in odd places that aren't out in the open.
She can be really fun; however I do kind of hate her weapon. The charge up shot seems like it could use a little buff and you have to be pretty close for the other and it takes a couple seconds before it gets good.
After playing her for a while now, the only thing I'd actually like to see is the charge up shot buffed a little. Either it charges faster, is bigger, or does more dmg. Pref it charges faster.