I used her in a game last night and she was very useful. But there is always a bit of a gamble to get the best out of her.
My Tara crew had 2 Void Wretches, 2 Death Marshalls, The Nothing Beast, Karina and Taelor.
Marshalls dive in and bury enemies,
Karina then uses her 'Energies of the Void' to give a buried model FAST and uses 'Flames of the Void' to set the buried models on fire (+2 burning). Or uses Energies again, whichever.
Void wretches then spend both their AP on 'Void Maw' which is an attack that targets buried models for 2/3/4 HOWEVER the Void Wretches' 'Time is Meaningless' ability means all duels vs FAST models receive :+fate
So that's Karina and Wretches happily holing up in an attic somewhere causing trouble for buried models. Leveticus, Bete Noire and the Dreamer all get murdered when they thought they were safe.