remove 1 turret
The two turrets are fine as a distraction, unless tanks are around to destroy them quickly. It's far easier for players to kill the turrets than it is for the turrets to kill the player, and if they're that great a problem, it's with you trying to take her on alone or your healer not providing enough support.
and lower her basic attack damage or lower the range its dumb fast she kills
But then she'd just be Zero Cool without the healing. If you want to kill Gizmo then Daemon and most tanks can take her out with little issue if they stay in her face.
and her turrets are overpowered
In what way? Is their damage too great, their rate of fire too fast, their range too great, their targeting too quick, their cooldown too short?
My advice is to lure enemies away from their range, or get behind cover so you can take out opponents and leave Gizmo waiting on a cooldown. Then all she's left with is her sucker bomb and a defensive bouncepad which - by the time she uses it - will be too late if you've been playing smartly.
A lot of the lessons you learn from shooters apply to ranged characters in this game, "duck and cover" being one of the key elements to countering them. ^^
I actually agree that she needs a little bit of nerf, specially to her rage which is kinda crazy, and even crazier with the mod. but, the problem is not with her turrets. They are way too squishy and can be taken out easily. The thing is, if the enemy team leaves gizmo alone, she can easily outdamage everyone by at least twice as much damage. So the enemy needs to focus on her, as much as they would on the healers.