Such situations are ALWAYS unique in their many details…Details that are never supplied in the scenarios for the simple reason that to do so would require writing a book instead of an internet posting.
Things you’ve left out are how this woman feels about having so many children…what is the role of the husband in all of this…etc…
Because these details cannot be known in sufficient detail on a public forum…and also because the function of a public forum is to provide public answers, we must state categorically that ABC is never permissible…
Your question here moves from the realm of the “law” and toward the idea of God’s mercy. It moves from the area of "normative teaching, to the needs of a given unique individual (or couple) in a given unique circumstance.
Here, I would simply make this observation. God granted His clergy the power or bind or loose sin…Confession, that is the sacrament of Reconciliation, is the place we go to discuss and deal with our sins and our struggles…
A person who finds themselves in the circumstance you outline here, needs to have the (name removed by moderator)ut and the guidance of a good regular confessor.
The Church’s teachings are firm and they are good. God’s mercy to those who seek to follow Him with all their heart is endless.
So - could a good confessor ever allow for an exception? Anything is possible…if the unique situation warrants it…
But I stress this above all…IF THE UNIQUE SITUATION WARRANTS IT…
and if it is seen (by Christ’s minister in confession / counseling) to be warranted…then it should not be discussed by the participants with anyone else so as to not cause confusion or sin by others.
I trust I have been sufficiently obtuse…
Peace
James