Yes, Mary has a special relationship with God. Yes God listens to the prayers of the faithful. But even in such context "just do these prayer rituals for five Saturdays and you're guaranteed saved" rings suspicious and hollow and is not merely a surface level critique at all. Even if done in faith, It doesn't sound that far removed from a Catholic version of OSAS. "Well, I've done my Five Saturdays, I'm saved! Time to kick back and relax!" Nowhere in scripture or tradition does God or Jesus ever imply a doing of a set of rituals for a set amount of time and achieving instant salvation. God, Jesus, the saints and Church Fathers all portray a long hard narrow path, carrying one's cross with stoicism and dignity in the face of hardship and sorrow. Not "do some rituals for a set number of times and you're done." Jesus may love his mother, but to change a road of hardship and struggle throughout the history of the church to a super streamlined just five ritual sessions over five days and you've won the ultimate battle with Satan, just for his mother, is not doctrinally sound, no matter how perfect or how much favor she curries. Even Elijah had to struggle and be a mighty prophet before God took him up to heaven. Enoch walked with God for 300 years before he was taken up to heaven. Mary herself was assumed up into Heaven, and as you yourself have outlined, went through horrific tribulation and sorrow before acquiring this privilege. I've read enough stories of Saints being put through the wringer on a spiritual and literal physical level, to view "five days and your done" with absolute disdain.
"But if they had real faith, they'd continue their struggles after the Five Saturdays…" No. She said:
That's it. No extra clarification or details. If there is/had to be some sort of "by the way, don't stop being a struggling Christian" addendum added by the church, it makes such a bold promise pointless. God's ultimate plan is for all of us is to take up our crosses and follow him, and everything that implies. Overriding this plan in favor of five days of rituals and done, even for his perfect loving mother is not sound doctrine. I'm not being antagonistic towards you out of spite or bad faith. I legitimately believe that this is questionable at best, and outrageous at worse, doctrine, no matter how close Jesus and Mary are. As I outline earlier, God has a plan: a plan that he won't just drop or alter just for his mother. At best his mother takes on a great role in his plan.
Even given Mary's favor with God, and even given La Salette, she would still glorify Him, not herself. She is the first and best Christian. As the first and best Christian, she would not say "I will save the world," Can you honestly think of any other saint or martyr giving themselves such glory and/or saying such a line? As Christians, saints or not, all glory goes to God. Period. Even if she is special among saints, she is special because of her faith and godliness within the context of how a Christian should follow and have a relationship with God. She would say "My son will save the world." She would point to her son, not herself. Even our icons of Mary with the baby Jesus always has her pointing towards him.
No, I don't think this is a gift. I think you want the prophecy of Fatima to line up badly enough that you are willing to say "well, even if Orthodoxy is not the True Chruch, it's close enough, so the Fatima prophecies are true."
The impression I've been getting is that you think Jesus and Mary's relationship is so special and extraordinary, that it is enough to outright override doctrine. Which I respectfully disagree with.
You're going to have to come up with a better argument than: "Mary is perfect and special and God loves her so much that he's willing to throw doctrine and proper Christian behavior out the window."