Some questions about the name 'Nienna'

So...I realize that Nienna's name derives from the Quenya for 'tears' and that all the wikis translate it as 'she who weeps' or something like that...But, I'm wondering what the etymology of it actually is. How does the root 'nei' turn into 'nienna'? And does it really mean 'one who weeps' or does it have more to do with tears themselves?

And here's the second, related, question: I'm wondering if there is a way to legitimately blend this name / concept / root with the Quenya for 'joy' or for 'blessed' -- seeing as the mingling of sorrow and joy (and final transformation of sorrow to joy) is so central Tolkien, I thought a name that holds the two concepts together would be really neat....but I don't have the etymological chops in Quenya to do so.

Thanks for any input on either of these!

The exact literal meaning of Nienna is not, as far as I know, attested or explained anywhere. Likewise we do not know what are the components of the name beyond the root √NEJ "tear".

The word nie "tear" derives from √NEJ (note: this J is IPA [j], like the first letter in yes), from a primitive form ✶nejē, which in Quenya simply becomes nie. I am not very well versed in Quenya historical phonology (Sindarin is my forte), so I cannot really explain this better I'm afraid.