I think that either your molly is not pregnant because if she was she would have had the fry well before now or that your molly is not a normal black molly but a baloon molly. Other than that there is no information i can give you. Mollies have their fry every 4-6 weeks if the female has been fertilized by a male. I have never seen a molly go longer than 6 weeks to have fry. Other may have differing experience and may be able to share that with you. HTH
She isnt being chased or anything like that is she, or you put her in a breed tank of some sort? I keep saying this, but if the fish are stressed they will abort giving birth and so can put it off...?