She is acquainted with grief, and mourns for every wound that Arda has suffered in the marring of Melkor. So great was her sorrow, as the Music unfolded, that her song turned to lamentation long before its end, and the sound of mourning was woven into the themes of the World before it began. - VALAQUENTA
She mourns for every wound, every grief. I don't believe it's is explicitly stated if she is a permanent state of weeping :- one would hope not as that's a pretty poor way to spend eternity!
Although everywhere reference in the Silmarillion (11 times she's mentioned) she is crying.