That's an old bug and shouldn't exist in the latest version. I built a safeguard against it, though. Just save and reload and the duplicate will be gone.
If a girl is recruited then she's either Shattered, Broken or Rehabilitated. If she's Shattered or Broken then she'll be available to send to the rehab centre (just go to the centre and select "admit a patient"). If she's rehabilitated then you can't re-rehabilitate her.
The character select UI will be getting an overhaul in coming updates to display more information on each character :)