I just caught up on this thread.
I think one of the two Italian men (not Sereno, and I can't recall the other guy's name) met and sweet-talked Ruth. She was titillated by the attentions of this man; however, he was grooming for sexual slavery. An upper-class, Waspy girl would probably be a good draw to a brothel.
He talked her into meeting him the night she disappeared, probably by telling her he wanted to run away with her. He said not to take anything that might have been traceable back to her (such as her sorority pin, watch, keys, etc.). She ditched the dorm key on the stairs after locking her dorm room, and she dropped her car key outside.
The testimony of one or more of the four guys at the OSHP officer's murder trial said they drove and picked her up, as if it was just another errand they were running. When the one man she was waiting to meet arrived with three other guys in the car, she panicked and tried to run away. He forced into the car and drugged with the "hypo" (the guy was prepared). She ended up in a brothel for a time, until the Pinkertons found her. The family was mortified, institutionalized her, and later let her quietly come home.
There was a note from one of the police officers (from a survey taken after the Conn murder trial) stating a woman reported that several of Ruth's college friends visited Ruth while she was in an institution in Cleveland.
I wonder if any Cleveland mental institutions/sanatoriums that were around in 1937 are still around today and if they still have records from that time. It might also be helpful to track down some of her sorority sisters and see if they told family members about what happened to Ruth. Hmmm...
My apologies for failing to remember names here. I'm totally drawing a blank on some of them.