Is Mary Mediating All Graces a Dogma?

If the title means something more than what we might be able to attribute to Abraham, if it means that not only is Mary a kind of proximate cause of the incarnation, but that all graces are in some sense, we can set aside whether they're moral or physical. Does it seem fitting? Does it seem probable? Absolutely. Do we know it with certainty? That seems much, much shakier argument. Any thoughts on that?