Based on a true story, which is even crazier!
The case of Dee Dee Blanchard and her daughter Gypsy Rose. Gypsy murdered her mom with the help of a man she met online.
From Wiki -
Gypsy Rose, according to her mom, suffered from leukemia, asthma, muscular dystrophy, along with several other chronic conditions and had the "mental capacity of a 7-year-old due to brain damage" she had suffered as a result of her premature birth.
Investigations into the murder found no evidence of the claimed disorders. One physician suspected that Dee Dee suffered from Munchausen syndrome by proxy, a mental disorder which causes a parent or other caretaker to exaggerate, fabricate, or induce illness in a person under their care in order to obtain sympathy or attention.
Dee Dee had slightly changed her name after her family, who suspected she had poisoned her stepmother, confronted her about how she treated Gypsy Rose. Nonetheless, many people accepted her situation as true, and the two benefited from the efforts of various charities.