it seems as if Nieniel was stricken with something like depression. In my readings of classical literature and such, the Brits had a tendency to show characters exhibiting physical signs of a problem for something that is wrong spiritually.
That was always the impression I had when reading that piece too. As a reader you know something is dreadfully wrong, so it is easy to overlook the fact that Nieniel is sad rather than looking forward to the birth of her child.
Don't forget, also, that prior to meeting Turin, Nieniel had forgotten her whole past. To lose your identity would take some getting over, and though someone might get over the initial shock fairly quickly, there would always be a questioning of who you are lingering behind. This latter doubt most likely would cause depression over the course of a year or so. If the same thing happened to me, I think I would feel guilty at finding love, knowing I could well be married to someone else somewhere.
As for the rest of the sentence... Like Grondy suggests, Tolkien was giving us the information of two sentences in one. I think you will find this quite a lot in the Silmarillion. Take for instance my all time favourite Silmarillion paragraph composed of four sentences....
The sons of Hador were Galdor and Gundor; and the sons of Galdor were Hurin and Huor; and the son of Hurin was Turin the Bane of Glaurung; and the son of Huor was Tuor, father of Earendil the Blessed. The son of Boromir was Bregor, whose sons were Bregolas and Barahir; and the sons of Bregolas were Baragund and Belegund. The daughter of Baragund was Morwen, the mother of Turin, and the daughter of Belegund was Rian, the mother of Tuor. But the son of Barahir was Beren One-hand, who won the love of Luthien Thingol's daughter, and returned from the dead; from them came Elwing the wife of Earendil, and all the Kings of Numenor after.
Genious or jumble???? In my opinion genius. In just four sentences he manages to mention:-
The names of 21 people and 21 different relationships between those people.
The fact that Turin was the Bane of Glaurung.
That Beren had only one hand, and that he managed to return from the dead.
That they were the descendants of a line of kings.
I challenge anyone else to manage so much in just four sentences.