@KMFalcon maybe (even though you hate chaol and don't ship rowaelin) she can have a drunk one night stand with one of them or just a random guy she doesn't know. There's also the option of Nox Owens reappearing from wherever he went or rape if you wanted to go down that path. Something could happen to Dorian to make him not mental for a little while and thus able to create said child. Or if nothing else works the ghost of Sam could reappear for a while and then disappear after the child is born.
If worst comes to worst there's always the option of creating a new character, adoption or her having the child for someone else and then the parents dying
Hoped this helped (ill check out your fic btw). If you don't like my suggestions i wont be offended, but feel free to use them XD