Thank you. I have no problem with your characterization. She wasn't saved or regenerated [born again] when God opened her heart. God was preparing her heart so that she would receive the word from Paul --- and that word would eventually accomplish those things in her.
This is the finer point of the Roman Catholics and the Protestant Reformation and the very thing that separates true Catholics from true Protestants. Catholics call this cooperation. The Reformers didn't buy into it.
We know God prepared the heart to hear the word and that preparation must be perfect. We know faith comes from hearing the word. If God prepared Lydia's heart so that she would receive the word from Paul, do you think she would not have accepted it?
It's this preparation that is the new birth.