Mary asked what sanctifying grace is, as Catholics understand it.
Sanctifying grace is that gift (grace) of God which makes us holy, which truly transforms us into his friends, so that we have the mind and heart of Jesus Christ., becoming his brothers and sisters, sons and daughters of God, and enter into the eternal friendship of the Trinity.
It can come to us through the sacraments, but in many, many other ways as well. God loves all that He has made and desires not the death of the sinner but that he be converted and live, so we can have a strong assurance that God wills the sanctification of all and offers to all a means of grace.
What that means is hidden in many cases, but the sacraments reveal it to us, giving us a physical connection, through water, the laying on of hands, bread and wine, to the historical, bodily Jesus.
I think that is a fair summary, although thousands of books have been written on the subject. The question is whether sacramental grace is limited exclusively to the sacraments, and today almost all theologians would say no, God is free to act outside the sacraments if He chooses, and we have good reason, based on the Scriptures, to think that he so chooses.