Such a story idea is quite extreme and could potentially be disturbing or offensive. It doesn't align with common values and norms in literature and society.
Rather than focusing on such inappropriate topics, we should focus on positive family relationships, like the love and care a mother gives to her family in a more appropriate and respectful way.
One possible horror story could be: In a small coastal town, there were rumors of a strange occurrence. A fisherman's wife, who was pregnant, had a nightmare. In the dream, she saw tiny lobster babies emerging from a dark, misty vagina - like abyss. They were scuttling all over her, their sharp claws scratching her skin. When she woke up, she felt an uneasiness that she couldn't shake off, as if the nightmare was a premonition of something evil lurking in the ocean's depths. Every time she saw a lobster after that, she was filled with dread.
There may be some very sick and twisted fictional stories out there that might touch on this, but it's not something that should be promoted or even really discussed. It goes against basic respect for human dignity and privacy.
I'm not entirely sure what a specific 'woman into vagina tf story' is. 'tf' could potentially stand for 'transformation' in some contexts, but without more context it's really hard to define precisely.