I've tried to help her see her way through this but her theology doesn't allow her to process the ideas the same as I do. For me, I echo John Piper's sentiment, "O how sweet are the designs of God in the sovereign salvation of hardened sinners!"
This was his closing line to this short but great post on God's Sovereignty, Paul's Conversion.
Ponder the conversion of Paul, the sovereignty of Christ, and what Paul's sins have to do with your salvation.
Paul said that God “set me apart before I was born,” and then on the Damascus road “called me by his grace” (Galatians 1:15). This means that between Paul’s birth and his call on the Damascus road he was an already-chosen but not-yet-called instrument of God (Acts 9:15; 22:14).
This means that Paul was beating and imprisoning and murdering Christians as a God-chosen, soon-to-be-made-Christian missionary.
Lord, they themselves know that in one synagogue after another I imprisoned and beat those who believed in you. And when the blood of Stephen your witness was being shed, I myself was standing by and approving and watching over the garments of those who killed him. (Acts 22:19-20)
The call on the Damascus road was apocalyptic for Paul. It was not a still small voice.
As I was on my way and drew near to Damascus, about noon a great light from heaven suddenly shone around me. And I fell to the ground and heard a voice saying to me, “Saul, Saul, why are you persecuting me?” (Acts 22:6-7)
There was no denying or escaping it. God had chosen him for this before he was born. And now he would take him. The word of Christ was sovereign. There was no negotiating.
Rise, and go into Damascus, and there you will be told all that is appointed for you to do. (Acts 22:10)
This kind of sovereign choice before he was born, and this kind of apocalyptic call on the Damascus road mean that God could have prevented Paul from beating and imprisoning and murdering Christians. He could have called him earlier.
Damascus was not Paul’s final, free will yielding to Christ after decades of futile divine effort to save him. God had a time for choosing him (before he was born) and a time for calling him (on the Damascus road). Paul yielded when God called.
Therefore the sins that God permitted between Paul’s birth and his calling were part of the plan, since God could have done Damascus sooner.
Do we have any idea what the plan for those sins might have been? Yes. They were permitted for you and me—for all who fear that they might have sinned themselves out of grace. Here’s the way Paul relates his sins to you.
Formerly I was a blasphemer, persecutor, and insolent opponent. But I received mercy . . . for this reason, that in me, as the foremost, Jesus Christ might display his perfect patience as an example to those who were to believe in him for eternal life. (1 Timothy 1:13, 16)
O how sweet are the designs of God in the sovereign salvation of hardened sinners!