Just learned of the existance of Verathiel from your blog and now I'm slightly obsessed with her! Anything else from the DIM campaign that is cool?
Hm lets see. Spoilers inbound!
The current final quest of DIM centers around Diablo using her to manipulate a Shard. She's been being tortured both mentally and physically by him ever since saving the player at the end of the Skarn fight. (Worth noting that by this point it has been apparent years of constant suffering from first Skarn, and now Diablo. Verathiel was nearly dead when we meet her for the first time.)
Verathiel's backstory, and Diablo's torment of her are covered in Her Comic which I highly recommend if you haven't read already. It's not very long but jam-packed with goodies. It also leads directly into the DIM quest.
Before creating her legion, Verathiel was primarily a mason who sang new worlds from the Worldstone. Because of this, Diablo is able to use her to sing again to a corrupt Shard of the stone, this time with the intent of unmaking Sanctuary. It's a complete reverse on what Inarius and Lilith did to build the world in the first place.
Singing to the Stone again is pretty much the final nail in the coffin, and she breaks.
After fighting her, players can choose to spare Verathiel, and if so she will join you in battle against Diablo. However, she will then be re-corrupted mid-fight and attack you again, entirely against her own will. Given that she begs you to put her out of her misery the first time you beat her, it might actually be kinder both to her and yourself to kill her rather than spare her. Kind of an interesting example of the story diverging (but not actually) in the game. No matter what the player chooses, she ends up destroyed. Makes me wonder if they've got anything else in store for her.
One of her swords can also be found and used in D4!