I don't understand why that idea is scandalous or upsetting to anyone. God favored Mary, just as the Angel Gabriel proclaimed, and God has the Power to do whatever He wishes, to make His will known on this earth.
“The Catholic Church teaches that Mary is the only human created sinless,”
Oh, I am aware of what they teach. It just isn’t Biblical. There is One Person who is sinless and it isn’t Mary, the sinner who needed a Savior.