The other plan she had for Legion was to rely on Ghaster. From the information she acquired from the squad that went to the Gattling plane, lightning might be able to harm Legion. This is because the child of the plane was able to wield lightning and the disease disappeared after the storm of lightning that the Celestial Supreme created. Either Legion was afraid of lightning or he was pretending.
If he was pretending that means he worked together with Celestial Supreme who created the lightning storm as a façade to kill the Celestial of Knowledge. If the two of them worked together, that means the Celestial of Lightning must be capable of restraining him. So either way, Lightning is still useful against Legion.
That's why Salvini planned to convince Ghaster to help her since he was related to Soverick and can wield Lightning. But now she is sure he will not even bother to come near her or entertain her request at all.
