They swapped bodies

When Lisa awoke, she felt cramped, and damp. Wherever she was, it was unpleasant and dark. She tried to get out, but her body felt a lot more, bulbous than normal.

"Don't tell me the tea did this to me!" She thought.

Lisa's body was panicking. Her stomach was engorged, to the point where it ripped her dress! That wasn't the worse part, as she felt something inside her push her about! It wasn't a pleasant feeling, especially since it was the slime's first time feeling what it was like as a human.

The slime knew it was in a new body, the librarian who drank it, to be specific. The slime also reasoned that 'Lisa' had to be somewhere. Thankfully, the slime had Lisa's smarts to put those together, as it tried to calm down whatever remained inside Lisa. It brushed against Lisa's big tummy as it admired the soft touch of her hand against its new body.

Lisa stopped, as she felt something. It was like something rubbing the roof of the place she was in. It was... calming, as she relaxed and cooled down. Slowly, she turned into a more watery state, which could easily exit this place. After a while, she felt herself trickle out. As she looked back to where she cane from, she saw... herself! She was exiting out of her own body!