Hi Kate, I'd like to provide you with my thoughts on this.
No, God did not create sin, but we were born, in sin, thus having what we know as Adamic Sin, or Sin Nature (Romans 6:14-16).
Because of that, Romans 3:23 says that ALL have sinned, and fallen short of the glory of God. That includes Mary, for she is as human as everyone else.
I know that you believe in Immaculate Conception. She must after all, be sinless, in order to give birth to the Son of God but there are holes to that doctrine.
1st - Do you recall Jacob wrestling with the Angel? We believe him to be none other than the pre-incarnate Christ, so if He is the 2nd person of the Godhead, Mary doesn't have to be completely sinless.
2nd - Jesus' incarnation involves Him aquiring a human body... and He must be in the line of David. That means Jesus is completely human... not some burning bush of a body where if one touches Him, s/he will instantly be incinerated. He is God in human form.
Fully God and Fully Man.
And that body, arguably, is infected with Original Sin. That is why He is, at all points, tempted as we are, but did not sin (Hebrews 4:15).
3rd - and finally, why didn't scripture tell us anything of Mary's sinlessness? Tradition, claiming that it fills the holes scripture did not speak of is no excuse.
The Bible says that ALL... have sinned ... and that doctrine contradicted clear reading of scripture.