There could be situations where a lesbian - identified woman has a platonic friendship with a man that might be misconstrued as something more. For example, they might work on a project together very closely and people assume there is a romantic or sexual element. Also, in some cases of trauma or significant life events, her view on relationships might shift temporarily, and she could find herself in a situation where she has some form of interaction with a man that she wouldn't have considered before.
One possible reason could be that she has discovered new aspects of her sexuality over time. Maybe she was in a heterosexual relationship because of social expectations, but as she grew, she realized an attraction to women.
Maybe she herself is still in the process of fully understanding her sexual orientation. She could be bisexual but confused, and end up in a situation that looks like 'cheating' from the lesbian perspective. Another factor could be family pressure. If her family is very traditional and wants her to be in a heterosexual relationship, she might succumb to that pressure at least for a while.
A curse is another common factor. In some stories, an ancient curse placed on a family or an individual for some past misdeed might result in a man turning into a woman. The curse could be activated by a specific event like reaching a certain age or entering a particular place.
Another reason could be related to mental health issues. If a woman is suffering from a condition like bipolar disorder and has an episode, she may become violent towards a man without full control of her actions. However, this is not to excuse violence but rather to understand some of the complex factors that could lead to such situations in stories.
Scientific experiment gone wrong. In a science - fiction type of story, a scientist might be working on a new technology related to gender transformation, and something goes haywire during the experiment on a male subject, causing him to turn into a woman.
One reason could be self - identity. The man may have always felt that his true self was female. Another reason might be influenced by the people around him. For example, if he has many female friends and is exposed to their experiences, he might start to identify more with the female gender.
In a story, one possible reason could be self - discovery. Maybe she has been suppressing her true feelings for a long time and finally realizes her attraction to women. For example, she might have had a chance encounter with a woman who makes her feel things she never felt before in her marriage.
Magic or supernatural powers could be another reason. Maybe there is a magical object that, when misused by a man, causes this transformation. It could also be part of a grand design by some higher - power entity in the story's universe to teach the man or society a valuable lesson about gender and pregnancy.
It could be that the man was dancing too close to her and she felt invaded or harassed, so she reacted by punching him.
One possible reason could be revenge. If the woman feels wronged in the relationship, she might wrongly think that blackmail is a way to get back at the man. Another reason could be financial gain. She may believe that by using sexual blackmail, she can get money or other valuable things from the man.