Technically she didn't order an assassination, as the curse didn't kill Einion's wife. In fact, it did the opposite, it made her unable to die despite the extreme pain and damage to her body that she inflicted on herself because of the madness it caused. Einion is the one that killed her, although it was less murder and more taking a suffering loved one off of life support.
I don't think Valledia has anything to do with Talia Gossam. Talia killed herself after a demoness convinced her that suicide would be an easy escape from her profound guilt over her affair with Baron Duin Halfmorn.