So you don't believe that any of the Persons of the Trinity ever acts directly to bestow a grace on a person?
Mary is to be credited with everything, since she bore Christ by the power and working of the Holy Spirit, and constantly attends to our needs. Without her, we would all be nothing, and with her God has willed her to be the effective bridge between divinity and humanity, not in the sense of Christ, were there was a union of nature to effect our redemption, but in the sense of a union of grace by the power of the Holy Spirit, to which we all hope to aspire, and to which she will lead her clients.
The Most Holy Trinity is not limited to working through Mary, but rather has chosen to do so. Ave fit ex Eva.
Read and imbibe:
http://www.catholicculture.org/docs/doc_view.cfm?recnum=4270