Mary, the Mother of Christ is favored by God the Father as St. Luke's Gospel tells us, by why is She Herself important, if at all, in the matter of Salvation? ( was it a once in a life-time hit by the Holy Spirit?)
I think Mary would help us in preparing us for the afterlife, by giving us some guidance.
Mary was no ordinary woman...God did not just go out and say Eeenie meenie minnie mo.... He had to choose a woman who was pure of heart, to the point of being almost saintly...
So the mother of Jesus, was and is, an almost perfect woman, as far as being holy goes.
This then enpowers her with some powers, I suppose....as a saint perhaps.
But for the most part, people are guided by Mary, to become better people. Mothers can use her as a role model for how to behave and how to be good, and how to keep their minds clean.
My grandmother was a great woman...kind, gentle and would give her shirt off her back, to anyone....my mother and my aunts, would pattern themselves after her. So it is, with Mother Mary.
She has been said to appear to some people, giving messages of good will and of what was to come.
So in that sense, I guess Mary would be an influence to guide us to salvation.
"was it a once in a life-time hit by the Holy Spirit?"
God is not man that he should use Mary like a man would use a woman for a one night stand. He does not use her and toss her away like some 'Christians' seem to think. Mary will be forever the mother of Christ, the spiritual mother of the Church, the Ark of the New Covenant, the final Davidic Queen (Mother of the King was the queen in Davidic kingdoms), and the New Eve. Her seed overcame Satan (See Revelations 12).
Without Mary we could not have Jesus become Incarnate. It was through Mary's flesh that Jesus became Incarnate. God commands we honor our parents in the old testament as one of the 10 commandments. Jesus forever honors Mary. Whatever Mary is, she is because of Christ the King. Thus, Mary magnifies the Lord with the graces that are bestowed on her. And, she offers these graces to her offspring the Church. She is the neck of the Body of Christ. Thus, all graces flow through her to the rest of the body.
I suggest reading "Hail Holy Queen" by Scott Hahn.