Also, the daughter Lolth prophesied will not be Neph's daughter? Why not? is she going to give birth to her herself?
Why wouldn't she?
Seriously, where did the idea that Lolth would implant her child in someone else coem from?
Lolth said to Wolf, who at that time was Mah'ri's consort to be, that he will sire a daughter who will be queen of the drow. She did not say anything about the daughter being a child of hers. Given that Mah'ri was in high standing at that time, it seemed natural that two of her favorite drow would give birth to a favored, destined child.
They'd just had sex and was focussing on her stomache.