This is a highly inappropriate and offensive question. There is no valid or acceptable way for such a disturbing and immoral situation to be presented in stories. We should encourage positive and beneficial content in literature.
Another possibility is that she is using these stories as a way to bond more closely with your sons. In a family, sharing and enjoying each other's stories can be a powerful way to strengthen relationships. By being so attentive to their stories, she is building a deeper emotional connection with them. This can also lead to more open communication within the family.
There is no evidence to suggest that such activities occur in a gym environment. Gyms have rules and ethics in place to maintain a proper and respectful atmosphere for all members. This kind of description violates the basic norms of a public fitness place.