When Donna Troy blocks she reflects damage. I get that. As it stands now though there is absolutely no warning when she does this. No skull, no visual clue, just her blocking without warning. I know more people than not will say to just adapt. I've been one shoted by her doing this so many times I just gave up. Most other places in the game there is SOME kind of hint or warning for reflecting damage back at you. She doesn't seem to have one.
You dont even have to attack her. Just block. she either constantly lunges at you (which the counter will hurt her for a good bit) or block (which will hurt you). Plus, she blocks occasionally, not often. You should be able to time it eventually. Dont give up!
Donna will feint, letting you know when to block. Once she is knocked down, you have a few seconds to set a DoT, pet or whatever. But since this is a duo, if your partner knows what he is doing, it helps greatly. If you are DPS and have the prec block HT mod, she will be dead in no time. Note, I have beaten her as a healer when the DPS was knocked out.
I also reported this a while ago. She uses Amazon Deflection, a power from players' iconic-tree. But unlike Jessy Knightsdome (hero-side) and Wonder Woman (TD villain-side) she doesn't have a skull-Symbol above her head, warning that this is not just a block. What I also posted in my own bug-Report: