Does the doctrine of the Immaculate Conception tell us anything about whether God knows "future continguent singulars," that is, things that have not yet happened and need not happen?
If the Blessed Virgin was preserved free of all stain of original sin as a special grace bestowed on her as the Mother of God, although she was not yet the Mother of God, then either God knew, in some fashion, that she would become the Mother of God, or He was somehow betting or hoping or guessing she would.
There are a lot of possible arguments that maintain both the Immaculate Conception and God's ignorance of future contingent singulars. The Immaculate Conception might be such that Mary's fiat would necessarily follow, or it may not have been freely chosen due to some other cause. Some argue, I've heard, that God knows some future contingent events -- the biggies, so to speak -- but not all of them. The idea that God really did such a grace without being sure His love would be returned seems to appeal to a lot of people these days.
The Catholic understanding, or at least my understanding of the Catholic understanding, denies both determinism and divine guesswork.