[the phantom]

Anyone up for a challenge? Let's try to turn this into such a discussion that they will have to move it back into the books forum.

Tolkien discusses Lalaith's revised role in the tale, HoME XVI, sec A, vii Narn i Chîn Húrin early drafts and revisions-

Lalaith was problematic in the early versions of "Narn i Chîn Húrin", as the younger sibling already provided the necessary final tragedy. It was an essential element that both Húrin and Túrin be isolated from the family, thus interaction with Lalaith was certainly not an option. The only place left for her was in the company of Morwen and Niniel, but Morwen also needed to be separate in the end. For a time I paired Lalaith with Niniel, placing them both under the dragon's spell, but upon reaching Brethil I could not shake the feeling of redundancy, as only one sister was necessary to provide the horrific finale.

In later drafts I omitted Lalaith completely, as it seemed the most obvious answer, but later I was struck by the idea that an early death would be more in harmony with the sort of tale I wished to tell. My first solution was for the dragon to cause her death at Nargothrond, adding another layer to his rivalry with the house of Húrin. However, such an event would not impact Túrin at all, as there was no logical way for him to receive such news while maintaining his ignorance of the identity of Niniel. It was most important to me that Túrin, as the primary character of the tragedy, experience this death if it was to be included. In the end I settled upon a childhood plague, simultaneously writing in the special relationship between Lalaith and Túrin, which had not been necessary before. The end result was to my liking, for it also served to make Lalaith more tolerable, as in the earlier tales she was somewhat annoying as an adult, with her incessant laughter and cheeriness through such awful events.