Most characters are mentioned in the clues. Most are dead anyway, so look at the tombstones in the graveyard mission.
She's explicitly stated (by Max himself) to have died at the end of the last game. The New York Minute ending where she survived is non-canon, and only changed a single frame in Max Payne 2 anyway.
There's a scene in there (MP3, I remember this) where he mentions the people he failed to protect who had died, dropped a few names, one of which was Mona.
[Edited by x_PhunshinE_x, 1/5/2013 10:39:58 PM]