Playing against Reva is a lot like playing Dreamer in 1st edition. People don't like the feeling that something is just gonna die and there's very little to be done about it. Which is the first part- get used to something just dying. I think a lot of folks are used to Soulstones, Armor, etc and just taking it on the chin. Can't really do that against her.
The additional challenge with Reva is it's much harder to hide what you don't want to die. Against 1st ed Dreamer it was easier to "feed" him models due to the more direct range he could hit. Reva has multiple attack vectors and can pretty much put more down as needed. Blocking line of sight and access are way big deals.
I've played her a few times now and I think a lot of the problem is the mental game. If the game isn't taken to her fast _something_dies every turn. Getting past that sick feeling is the first step to beating her.