The White Mage had used her magic, whiteout, and brainwashed nearly all of the Fairy Tail Guild. One of those brainwashed was Lisanna. The White Mage had ordered all of the brainwashed guild to go and wreak havoc

During the chaos, Lisanna managed to spot Lucy and took advantage by using her animal soul magic to turn into her lamia form and coiled herself around Lucy's body

While she was instructed to eliminate anyone who stood in The White Mage's way, Lisanna instead opted to try and hypnotize Lucy into joining The White Mage instead

Lisanna: Cups Lucy's cheeks so they lock eyes while she is still coiled around Lucy's body Don't worry Lucy, The White Mage didn't do anything to me but open my eyes… She can open your eyes too, just trust me… Let me bring you to our side so we can serve the White Mage together… we'll still get to be friends, still get to be together… she smiles as she says this in a soothing voice