Due to her special and unique connection, she already deemed the Blood Ocean and the seat of the god of the pathway of killing as hers. This is why Legion's existence felt like the existence of a thief to her.
It was a bad feeling to know that a thief existed nearby and not be able to do anything to stop them. She surely couldn't leave her fortress, or she would be torn apart by the blood beasts as soon as she steped out.
The alternative is to leave the spiritual dimension completely from within the fortress to hunt this killer in the physical dimension. But she can't do that because she doesn't know their identity or where they are staying in the physical world.
Even if she knew all of these things, there is still the matter of her killing lamp bearers and stealing from the church of justice to deal with.
