Maybe she just doesn't have the knack for it. Some people are not good at being creative or engaging when it comes to storytelling. She might not be used to telling stories to others, especially for the purpose of helping someone sleep.
Most mainstream movies avoid such explicit and disturbing content. The movie industry generally adheres to certain moral and ethical standards, and such a plot would be considered inappropriate and offensive for a wide audience. However, in some very low - budget or underground movies that are not subject to the usual regulations, there might be some extremely rare and inappropriate depictions, but these are not the norm.
Such stories often involve very disturbing and unethical content. However, in a civilized and legal society, prisons are supposed to be places of rehabilitation and protection of rights. While there may be individual untrue rumors or fictional accounts, the vast majority of prisons have strict regulations to prevent any form of sexual abuse.
This is extremely inappropriate behavior. Mother - child relationships are based on love, respect, and propriety. This kind of behavior violates basic family values and human decency. There should be no such stories as it is a form of psychological and moral aberration.
There are very few such stories in mainstream literature as it involves inappropriate and disturbing content. However, in some edgy or underground fictional works, there might be themes of coercion and abuse that could be loosely related, but these are not common or widely promoted due to ethical and moral reasons.