Let me break it down for you.
1. The Woman of Rev 12 gave birth to the Messiah. Do you deny that?
King James Version (KJV)
1 And there appeared a great wonder in heaven; a woman clothed with the sun, and the moon under her feet, and upon her head a crown of twelve stars:...
5 And she brought forth a man child, who was to rule all nations with a rod of iron: and her child was caught up unto God, and to his throne.
2. Jesus Christ is the Messiah. Do you deny that?
3. Mary is the mother of Christ.
Therefore, the Woman of Rev 12 is Mary the mother of Christ.
It seems really simple.