1. If your char gets onehit by Rey it says more about your char than about Rey. Looks like Rey is higher geared/modded than your char. Facing a toon with same gearlvl Rey usually is not able to onehit. A maxed out Rey can't onehit any char of my arena-team in 1st round. Never!
2. She IS balanced, yes she is pretty fast and hits like a hammer. But that's all she has to offer. With no taunter around her she is wiped away in a few blows. The fact that she is not viable on her own and that she needs other toons around her for protetion demonstrates pretty well, that she actually is balanced.
3. I don't say a fight against the usual metasquad Rey + RG/Han + the other usual suspect is always a piece of cake. But with the right strategy around a well-composed team with good leveled toons it is possible quite often to win. What leads me to
4. Most whiners demanding a nerf of Rey just don't have the right counter-strategy yet. But there are plenty of them. Instead of whining focus on farming an appropriate arena-team and the force will be with you.
My arena team has 3 possibilities to deal with her:
1. Keep her stunned while getting rid of RG
2. Damage her to a little more than half of her health and let make my Rey give her the final blow without activating RG's taunt.
3. Just damage her, remove RG's taunt with QGJ and finish her off.
And I'm sure there might be even more possibilites to deal with her.