Diversify your team. She’s remarkably easy to beat with a number of characters and compositions. You just have to be careful to not play the all-out focus-fire offense against her that works in most other situations.
She’s easy for a Resistance team. Ignore her, only attack with Finn’s stun. Use it every chance you can get. But otherwise ignore her, then when she’s the last one left use only basics so she gets a chance to take a turn and then lose her protection.
Alternatively, drop your fifth character and instead use 4 Resistance characters and Jango Fett. Then use his special to reduce her health by 25%. Since her bonus protection is directly based off her maximum health, this will drastically reduce the amount she gets every time she’s hit. If you even need to get a second special off and drop her to 50%, then you guarantee your win (as I said—Assuming you haven’t already won by then).
The longwinded point I’m making is that it’s natural to think she needs a change. But once you take a look beneath the surface you see that she works absolutely fine. Even the play style she’s intended to counter can beat her if you play right. Although some squads (Ewoks!) are just murdered by her outright. Don’t use those squads!