She stayed behind in Valinor while her husband Fëanor, angry at Morgoth for murdering his father and stealing his Silmarils, goes and takes the Teleri's ships by force, igniting the slaying of the Teleri. After Fëanor was murdered by Balrogs, most of her sons died in battle or suicide. Did any Valar or Maiar tell her about it, or was she blind to the whole thing?
I seem to say this a lot when answering your questions...
The affairs of Aman are left almost entirely unexplored following the Flight of the Noldor, so there's really no way to know.
It's certainly possible that she could have found out, through any number of methods:
- As you suggest, one of the Valar or Maiar could have told her
- Since most Elves are eventually reincarnated, it's possible that another dead Elf encountered one of them in Mandos, and then relayed news of that to Nerdanel
Related to the above, it's entirely possible that one of the Six (dead) Sons of Fëanor were reincarnated and told their mother themselves. This categorically not true of Fëanor, since we're told that his spirit will never leave Mandos:
Then [Fëanor] died; but he had neither burial nor tomb, for so fiery was his spirit that as it sped his body fell to ash, and was borne away like smoke; and his likeness has never again appeared in Arda, neither has his spirit left the halls of Mandos.
The Silmarillion III Quenta Silmarillion Chapter 13: "Of the Return of the Noldor"