Mary’s sinlessness doesn’t affect his concupiscence, but by her extreme devotion and with the special aid of God’s grace she overcame these struggles.
One instance that proves that Mary can sin (but did not) is her inquiry to Angel Gabriel.
"Mary said to the angel, "
How can this be, since I am a virgin?"
(Luke 1:34, emphasis mine)
This is a crossroad for Mary. Zechariah had failed in this part. Instead of believing Gabriel’s message, Zechariah doubted and emphasized his own senility and the untimely redemption of their public shame. By this way, Zechariah had sinned with “unbelief”.
Mary, on the other hand, is only a wrong step more to fall in the pit of sin, too. She questioned the message in the matter of virginity, but with belief in the message. If Mary had inquired the “how” of the incarnation in the wrong attitude and disposition, Mary would have sinned, too, just like Zechariah. But Mary just said, “How can this be, since I am a virgin?”. That is true in her part and that’s interesting with Mary. Mary admitted her own inability to produce due to her virginity (even if she knew she was betrothed to Joseph, who has the possibility to impregnate her in the future), and Zechariah denied his own ability to produce in the pretext of his (and Elizabeth’s) senility. Mary gave the question the right way and in faith. Zechariah in the wrong disposition of unbelief. See the difference? It seems like Mary is standing at the edge of the cliff. Probably because this is the Annunciation, a very special event. Satan might be there to tempt the Blessed Mother to say “No” (Have you read that Mary was very perplexed at that moment?)
So it is understandable that even the Blessed Mother is exposed even to the perils of life, because this earthy life is a valley of tears and temptations for us. But with God’s grace and His preventive salvation to her Mary was preserved, but as I said, that doesn’t take away her freewill. It is only by God’s grace that she had endured and stayed with the right.
So Mary isn’t exempted with concupiscence. Mary might have been tormented with various temptations also at Calvary. Read my blog write-up,* Mary Vs Atheism.*
marynodded.blogspot.com/2008/10/mary-vs-atheism.html