Your words carry the weight of a man who is holding both deep pain and deep hope together. There is a very real tension in what you have written, a place where the justice of God and the mercy of God seem to pull in opposite directions. You know the scriptural permissions that would allow you to walk away, yet your spirit keeps being drawn back to the throne of grace, asking for something far greater than a legal release. That very prayer, that desire for her salvation and restoration rather than simply for your own freedom, is not a small thing. It may well be evidence that God is already working in you to will something of His own heart.
The matter of a hardened heart is what we must look at squarely. When a person stiffens their neck against God and against clear truth, a terrifying process begins. In the beginning, it is the person themselves who hardens their own heart. Every time the Spirit brings conviction, every time a godly plea is sent or a memory of truth stirs the conscience, and the person pushes it down and says no, they are adding another layer of callousness. They are choosing to be their own god, deciding good and evil for themselves, just as the old rebellion in the garden promised a false freedom that only leads to death. And what you are describing, the refusal to reconcile, the cutting off of communication, the unremorseful breaking of vows, looks very much like a heart that is strengthening itself in a devastating position.
There is a sobering point that comes after repeated self-hardening. What begins as a person repeatedly hardening their own heart can eventually lead to God Himself confirming that state. The language used in Scripture is that God makes firm or stiffens what the person has already chosen. He does not create the hardness out of nothing, but He essentially says to the person, "This is the position you have stubbornly chosen, and I will strengthen you in it." It is a judicial act where God removes the restraints, and the person is finally given over fully to the desires of their own rebellious heart. They become firm in their rebellion, so firm they cannot turn. They go past the point of having any inclination to repent, not because grace was insufficient, but because they have so persistently refused it that the capacity to hear is lost. That is the danger that hovers over anyone who keeps saying no to God.
Yet, you are right to still plead for mercy. As long as there is breath, we do not know for certain that the final line has been crossed. But we must be clear that the kind of change you are asking for is nothing less than a resurrection. It would not be a surface-level sorrow or a frightened confession that just wants to escape consequences. Many people will admit to being a sinner when caught, yet their life shows no fundamental turn. True repentance is a change of mind that produces a change of life. It is a heart of stone being supernaturally removed and replaced with a heart of flesh that beats for God. This is what Jesus meant when He said a person must be born again. It is not a renovation of the old self; it is a new creation. And this is what you are truly praying for: not just that she would return to you, but that through a profound encounter with the living God, she would be made a new person entirely.
This is why your question of wisdom is so critical. You are asking to choose the highest path, and that requires a heart aligned with God’s own. Paul spoke of having an enlarged heart for people, a heart that was opened wide even when the other side had shut down the flow of love. It was rare and precious to find someone else who shared that same genuine burden. The love you are describing, a love that would rather see her saved and made new than simply be free of the pain, resembles that enlarged heart. It does not excuse sin, but it longs for redemption over revenge. Working out this reality in your own soul, learning to fear God all day long yourself, is the ground out of which true discernment grows. If you ask for wisdom, the answer may well be for God to put His own burden deeper into your chest, a burden that continues to patiently suffer and hope and give witness to the truth, even when the situation looks dead.
There is no pretending that this is easy. The path of staying open to reconciliation when love has been rejected feels like a narrow and crushing place. But a heart enlarged by God is not ultimately pressed in and destroyed. The call, even in this, is to model a love that is compelled not by the desirability of the other, but by the character of the One who loved us while we were still His enemies. If you are to be a living epistle, then the story she reads of God’s faithfulness through your own patient grief may be the very thing that pierces the darkness at an hour you least expect. Do not take the day of salvation lightly. Today is the accepted time for every heart that is still beating. And while you wait and pray, let God do the deep work of sanctifying your own heart in this pressurized place, making your own hope and life the clearest portrayal of the gospel you can possibly offer. Your will is being laid down as you say "Your will be done," and that is the only safe place for any of us to be.