Vesa was in a frenzy.
She activated her Frequency while her mind was being externally influenced by the ghast. Whether it was due to this, some kind of self-preservation in her Frequency, or her not being in control of it, her Frequency completely dominated her mind and senses, forcing her into this crazed frenzy against the Ghast of Shorstone.
This did have the benefit of making her immune to the ghast's aura. However, this immunity came at the cost of her not fully being in control of herself, allowing her to remain unaffected by the ghast.
This frenzy of hers caused plenty of downsides. She was reckless, unaware of her surroundings, who was her enemy, and overall unable to control herself.
