Ah, I think I understand now what you're getting at here. To be honest, I need to pray and seek God's guidance on this as I've never read this passage with Mary in mind before but my initial reaction would be that Paul's making up for the lack of Christ's sufferings, even with the understanding of "not I, but Christ" is not in the same league as Christ's Redemption of Mankind. Similar in some respects, yes, and maybe even in the same "family" but I hope you'll understand my extreme caution in not wanting to attribute any kind of honor for Redemption to anyone other than Christ. My redemption and the honor, glory and worship due to my Redeemer is not something that I monkey around with lightly. I'm more than glad to honor Mary for being the earthly Mother of Christ, but this is a whole different level.
Yes not in the same league and Oh,My,DWACIOUS yes, I understand the anxiety.
SOME salve MAY be found in Philippians, “for it is God that worketh in you,both to will and to do.” Our part is the fear and trembling, of which I bet Mary did plenty, and not just at the foot of the cross.