Okay, so Phyllis told Nina she was ONE of her nurses. And it's safe to say Madeline was a fairly evil and intelligent woman... SO...

What if Harmony was one of Nina's nurse as well.

And what if Madeline knew Phyllis had split Nina's necklace- so she paid off or otherwise convinced Harmony to trade her own baby with Nina's and then put half of Nina's necklace on Harmony's baby before having Phylis send her off to her new family.

That would make Nelle Harmony's real daughter, and Nina's baby, Willow- and it definitely would have guaranteed that even if the child grew up, went looking and somehow found Nina, that Nina still would never get a relationship with her real child.

Willow would have been raised by Harmony with no knowledge or reason to ever go looking for her 'real' mom.

Harmony's pledge she gave Shiloh could very well have been that Willow was not her biological child, which could explain all her bad choices she made (based on feelings of guilt) and her weird, strained relationship with Willow.

Just a thought. Lol