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I'm not sure what, exactly, it is that you mean, but Really Was Born Yesterday would work if the character has No Social Skills because she was, well. Only just born.
I believe you’re thinking of “Born Sexy Yesterday”, which is a trope recognized by the wider culture that doesn’t have a page here under that name.
Some related tropes that do have pages: Age-Gap Romance, Wife Husbandry, Pygmalion Plot, Kiss Me, I'm Virtual
^ We have Naïve Everygirl though.
Oookay, my ability to recognize innuendo is seriously impaired.
Poor Things Little Mermaid My Stepmother is an Alien Splash
I'm told Born Yesterday is like this