We can debate Edwin's mommy issues all day, but it's a fact that Rosalind targets Edwin because she percieves him to be soft and naive. She knows Ian would've told her to kick rocks, and she only approaches Edwin if he doesn't take advantage of her at the "audition", or if he apologizes after the fact. In fact, the only way to access the Full Deal route is to display weakness at the start and not go full asshole, despite Full Deal being one of the darker routes in the game.
So she's not just begging for help from anyone who will listen, she exclusively targets Edwin if she thinks she can manipulate him with her sob story and sex. I'm not calling her a bad person, but she doesn't try to pull this shit with anyone else, because she knows it wouldn't fly. If she thought she could've gotten Ian to give her a leg up, she would've tried.
It just so happens that Edwin's own mommy issues and past struggles make him susceptible to Rose's tactics, and extremely sympathetic to her plight, which is a mirror to his and Vicky's struggles.