I think the baby probably technically holds dual citizenship.
Not according to the summary of Bahamian citizenship laws that I linked. She currently does not have Bahamian citizenship, but will have the right to become one at 18 if she registers for it. If she hasn't registered for it by age 21, she loses the right. Meanwhile she is a US citizen. BUT from the current perspective of the Bahamian government, Stern is her legal father by virtue of his name being on her birth certificate. Until a US court rules differently, and informs the Bahamian government that it has done so, the Bahamian government will presume her to be in the legal custody of her father (Stern). Until and unless that has happened, absent a formal demand from a US court to send the child and/or Stern back to the US, there's really nothing the Bahamian government can or should do. I still haven't heard of any such order emanating from a US court (presumably it's forthcoming though).