Perhaps these other insights of St. Faustina may clarify that picture of hell. She is convinced God sends no one to hell, a soul chooses hell/separation from God.
"Only the soul that wants it will be damned, for God condemns no one" (Diary, 1452).
She also notes that the fire and tortures do not come from God, they come from Satan. The soul chooses hell over God, and the conditions in hell are set by Satan, not by God.
Note where it says they feel God's anger? What they are feeling is God's anger and opposition towards evil, a feeling Satan can supply. It is not God's anger towards the individual.
St. Faustina is adamant that the heart of Jesus is filled with mercy, and that we should all turn to life/existence with him--not apart from him. So why did she write such frightening things? It was to show the great magnitude of God's mercy. Remember, we have a choice...God or no God. If the choice is no God, then there is Satan to sweep us up--and into a place designed by him, not by God.