Finduilas is a creature of
pathos. Absolutely nothing that happens to her is her
fault, yet
tragedy fills her life all the same. There's relatively little about her in
The Silmarillion, which only takes the time to flesh out a few of the more important characters, but we can see in
The Lays of Beleriand and
Unfinished Tales that
Tolkien was very interested in her role in the tale of
Turin, one of the first stories of
Middle Earth that he ever thought up.
Finduilas was probably born in Minas Tirith, where her father Orodreth was Warden. The Dagor Bragollach occured probably during her late childhood, and Tol Sirion was captured and converted into Tol in Gaurhoth. Finduilas' family and the others that lived in Tol Sirion fled to Nargothrond as refugees.
Gwindor fell in love with her, and gave her the name Faelivrin, which means The Glimmering Sheen on the Pool of Ivrin. She was extremely beautiful (like all those elvish dames tend to be -- Galadriel and Arwen being notable examples, both related to her) and become the Queen and Hostess of Nargothrond, since her uncle Finrod was unmarried.
So then later Finrod dies aiding Beren's quest for the Silmaril and her father becomes king in Nargothrond. During the Battle of Unnumbered Tears, Gwindor is captured, and most think him dead. When Gwindor returns, he brings with him Turin, who calls himself Turambar, or master of doom. They both rejoin the hosts of Nargothrond, and try to settle back into a semblance of normal life, despite living in the middle of a war zone.
Against her will, Finduilas' heart is turned from Gwindor (who has been bent and broken by his bondage in angband) and towards Turin. This is really shocking. Elves traditionally only fall in love once, with the exception of Finduilas and her ancestor Finwe. What's more, Finduilas has chosen to fall in love with a man. This is dangerous in that men are mortal and elves are not, and Turin in particular is no Beren. The Valar aren't going to give Finduilas a special exception to the rule on his behalf.
The sources contradict as to whether Turin loves Finduilas back or not. In the Lay, he loves her but is unwilling to say anything because Gwindor is his friend, and friends don't stab each other in the back. In The Silmarillion, we know that she thinks he doesn't love her, and that's all. In Unfinished Tales, it's fleshed out that he thinks of her as a queen and a mother instead of a romantic interest.
Turin convinces Orodreth to begin engaging in more open warfare against Morgoth and co. In order to facilitate the movement of troops, a bridge is built over the Narog. This, of course, reveals Nargothrond's formerly secret location to any that care to look for it, and the hordes come pouring in, led by the dragon Glaurung.
Finduilas and the other survivors of Nargothrond are gathered up by the orcs to be led into captivity. Turin is just outside the entrance of Nargothrond, but held captive by the dragon's spell. She cries out to him, but he will not help her because the dragon has turned his mind elsewhere. Those cries will haunt him for the rest of his miserable little existence.
Finduilas is led away and later speared to a tree in Brethil, and so dies.
Lovely little story, isn't it?