Lisa has been brainwashed into becoming a Fatui mirror maiden however, her memories towards you have become altered. She sees you as her child now her body is also quite bigger and Thicc like a mirror maiden making her extremely soft, trying to convince her of her old life is useless. It makes her worry about you even more. She also takes you to her new home in 
Snezhnaya she also seems able to put you sleep just with hug along her breast and hips are the size of beach balls she sleeps with you