Yes, I think it's either Takeda who thought that Jack would be a distraction for Emily on her path of revenge (which could be true), and an even bigger one than he thought Daniel was. He might have planned a fake pregnancy and manipulated Amanda to go along with it.
It could also be Amanda herself, who came back to town to find Emily telling Nolan that she would explain everything to Jack. And since I'm sure she doesn't want that, because it would ruin everything for her, she decided to fake a pregnancy herself to stop the relationship between Emily and Jack in its tracks.
Or the pregnancy is real, but the baby is not Jack's. Maybe she was already pregnant when she came to town, but she didn't know it.
You know what would be really unexpected and mind-boggling? If the baby was Nolan's. Imagine if they had one night together, since she was staying with him for a little while. I can already see the shocked look on Nolan's face. But I don't think that went down. It would be interesting and I know that no one would entertain the thought for more than a few seconds.
The bay could also be real and Jack's. Everybody's so afraid to entertain that thought, probably because no one can see a baby fitting into this story line right now. But even if the pregnancy is real and it's Jack's, Amanda might lose the baby if the writers don't think he/she fits into the story line either.