St. Faustina Kowalska was the first Roman Catholic saint recognized in the 21st century, and had had her visions and diary of Jesus suppressed by the papal office (which she had predicted would happen, or which Jesus had told her would happen) for about 25 years, before she was investigated and eventually petitioned for unbanning by Archbishop Karol Wojtyla – soon to be Pope John Paul 2! Thanks to his promotion of her, her focus (reportedly directed by Jesus) on “Divine Mercy” has been greatly advanced, and the RCC now celebrates Divine Mercy Sunday as the first Sunday after Easter–she has a direct following of at least 100 million devotees, and is sometimes even known today as “The Apostle of Mercy”! JP2’s successor, Benedict 16, instituted a World Apostolic Conference on Divine Mercy in 2008, and issued a Mandate on the Divine Mercy in 2009. (Which although I haven’t read it yet reportedly contains some “stunning” statements (as the publisher puts it) on how even Judas’ betrayal reveals God’s mercy.)
I have a suspicion from the confluence of notable universalists and near universalists involved here (her teachings were also the basis for a spiritual retreat booklet for modern RC women along with known Christian universalist St. Therese of Liseux for example), that she was also a Christian universalist. Her 700 page collection of diary entries can be found attached to this post, if anyone wants to work at checking it over for commentary.
Some interesting selections from her work (borrowed from a Wiki article on “the devotion of Divine Mercy”): those attending chapels set up for this devotion are encouraged to pray at around 3pm (when Christ died), “O fount of life, immeasurable Divine Mercy, cover the whole world and empty yourself out upon us. O blood and water which flowed out as a fountain of mercy for us, I trust in you. Holy God, Holy Mighty One, Holy Immortal One, Have mercy on us and on the whole world (repeat thrice) Jesus, King of mercy, I trust in you!”
The thrice repetition of “on the whole world” indicates maximum emphasis, the scope of which obviously includes everyone who has not yet accepted Christ’s salvation; and in her diary she reports Jesus saying to her on this topic of veneration at 3pm, “As often as you hear the clock strike the third hour immerse yourself completely in My mercy, adoring and glorifying it, invoke its omnipotence for the whole world, and particularly for poor sinners, for at that moment mercy was opened wide for every soul.”
That’s exactly what we Christian universalists do when praying to God; although to what extent she understood the “omnipotence” of God’s mercy “for the whole world”, I don’t clearly know yet. I just know what I would mean if I said that! 
St. Faustina-Divine Mercy in my Soul.pdf (1.55 MB)