Q:

Does "all have sinned" (Rom. 3:23, 5:12) include every single human being?

My mother and I go round and round on various Catholic vs. Protestant beliefs and in particular the Catholic belief in the pseudo-divinity of Mary. One item is whether Mary was sinless.
I pointed to Paul's statement:

Romans 3:23For all have sinned…

or

Romans 5:12…by one man sin entered into this world and by sin death: and so death passed upon all men, in whom all have sinned.

That would seem to include Mary among the "all". Yet her retort is the "all" would then have to mean babies in the womb, infants, etc., who weren't capable of sin. My thinking is Paul might have meant "all" as referring to those actually capable of sinning or old enough to know better.
According to the Catholic Church, what did Paul really mean by that declaration? Does "all" really mean "all"?

A:

According to Catholicism: Does “all have sinned” (Rom. 3:23, 5:12) include every single human being?
According to Catholicism the short answer is: No.
The two exceptions according to the Church were Jesus called the Christ and his mother Mary.

The belief that Mary lived without sin from the moment of her conception springs from Church tradition. It evolved over a period of time and was not formally defined as a teaching of the Church until 1854. It is not found explicitly in Scripture, but seems for Catholics to flow naturally from the testimony of Scripture that Mary was “full of grace” (Luke 1:28) and “blessed” (Luke 1:42).
In Catholic understanding, the belief in Mary’s “immaculate conception” does not say so much about Mary as it is about Christ’s saving power. We believe that God created the human person to be in God’s own image. Grace is more original than sin. Our natural state was to be “full of grace.” Sin is our universal experience, but it’s not what God intended for us in the past nor wants for us in the future. We are saved from sin through Christ. Mary’s being conceived without sin takes place in the context of the entire saving act of Christ. In being “full of grace” she is a model of what we human beings were intended to be and who we are redeemed to be through God’s saving power. She is the first sign of God’s victory over sin in Christ. - Where in the Bible does it say that Mary, mother of Jesus, is sinless? And if it is not in the Bible, why does the Catholic Church act like she is?

The Catechism of the Catholic Church explains it this way:

490 To become the mother of the Saviour, Mary “was enriched by God with gifts appropriate to such a role.” The angel Gabriel at the moment of the annunciation salutes her as “full of grace”.  In fact, in order for Mary to be able to give the free assent of her faith to the announcement of her vocation, it was necessary that she be wholly borne by God's grace.
491 Through the centuries the Church has become ever more aware that Mary, “full of grace” through God, was redeemed from the moment of her conception. That is what the dogma of the Immaculate Conception confesses, as Pope Pius IX proclaimed in 1854:

The most Blessed Virgin Mary was, from the first moment of her conception, by a singular grace and privilege of almighty God and by virtue of the merits of Jesus Christ, Saviour of the human race, preserved immune from all stain of original sin. 

8 Things You Need to Know About the Immaculate Conception

