As the leader of Annihilatus, she has enough skill to withstand a swing from one of Sasha's implements (that ended up smashing a table in half) without any harm done to herself when she tried to force Sasha into a "Magical Powered Kanamin" cosplay.
When the order came from the upper echelons of the Russian Orthodox Church to hand Sasha over to Fiamma, she decides to betray the Russian Orthodox Church, if it means to be with "her" Sasha.
In Volume 22, She was shown to be a immortal witch who had supposedly sacrificed her mother and elder sister for power. In Russian Folklore her real identity is a witch who devours other humans, and for humans the only outcomes when facing her are either run or be devoured. She possesses the 'Water of Death', which can melt away a person's flesh until only bones remain, and the 'Water of Life' which grants the drinker immortality.
She is also shown to be strongest spellcaster in the Russian Orthodox Church so far, managing to defeat all of the assassins sent after her by the Church after turning to Fiamma, without getting wounded herself. She defeated Bishop Nikolai who even used the 'Water of Death' on her like in one of the Russian Folklore tales where the witch fell into the spring that is the origin of the 'Water of Death', but it backfired as Vasilisa possesed the 'Water of Life' and ultimately healed the injuries as if it was nothing.