Lavagirl is one of the superheroes Max dreams up. She is the other young warrior who protects Planet Drool. She is uncertain of her own identity and purpose throughout much of the film. She has an explosive temper like Sharkboy, but is better at controlling it than he is and rarely gets very angry.
She is very kind and motherly, especially to Max. She, like any teenage girl, doesn't know her purpose or identity. She is shown yelling at Max for creating her with fire powers after burning his Dream Journal when she tried to read it. This made her very angry; hair bursting into flames and a fist burning hot. This has led her to the belief that she is evil and she just needs to accept it. She is also upset by Max pairing her with Sharkboy because they're not compatible. By the end of the movie though, she realizes that she is not destruction, but light. She becomes the healer of the planet and a force of light for all living things.
Her origins are unknown.
She can change herself into lava, which can be a problem when her leg detaches from her body while escaping plughounds. Things light on fire if she touches them or is near them. She can control lava in her direct vicinity and can shoot lava from her hands. She can shoot fire from her hands and feet to use as a way of shooting to a point above her. Her hair has a tendency to produce pink flames and her hands glow orange when she is angry or using a lot of power. If she dies, she can be revived by being thrown into an active volcano. Eating ice and falling asleep can cool her down.
She is very motherly to him and, him inventing her, appreciates his work. She does get mad at him for some decisions he's made designing her. She does forgive him, however, and he helps her realize she is light.