so it would be the lesser charge of wrongful retention and not abduction.
Its abduction no matter which way you want to dress it up.
they arnt married but his name is unfortunately on birth certificate
It does not matter if it is or isn't on the certificate.
she's not in a safe enough situation to stay and fight in the courts
If she is living in the UK then this is not an excuse. There are many support organisations to assist in "real" situations.
My advice to you is contact reunite.org as a matter of urgency and follow their advice to the letter. If you don't, then expect life to be hell for a minimum of three years.
Good luck. You will need it. By the way being involved in the abduction of a minor could land you with a minimum 2.5years in Poland. You are already assisting.