If you go to Luke 1:28 and look up the Strong's Greek for G5487 or Favored, it in no way means she is without sin. Noah found favor with God because he believed God, not because he was without sin. It says Noah found grace with God which means he needed it. The other sentence there saying his generations were perfect, just means his flesh had not been corrupted by the Fallen angels of Gen 6:1. The whole Bible is founded on the seed of the woman killing the seed of Satan. Abraham was a pagan, but he believed God and righteousness was imputed to him. Mary received the seed of God, but she was not without sin. Jesus is the seed of the woman. Jesus is the seed that kills Satan's seed, the Antichrist. It won't be Mary coming back in Revelation to kill the Antichrist and his followers. If Mary was sinless, we wouldn't need to sacrifice Jesus. God used many faulty people to accomplish His purposes. Jonah messed up 9 ways to Sunday, yet God used him for His glory. Mary was blessed beyond measure to be God's chosen vessel, but can we say John was blessed? John was the one Jesus loved. Peter? Was Peter without sin?
Mary had the unique position of needing her son to die for her sins in her place. Can you be joyous that your son is going to die to set you free? Peter said it would not be so when Jesus spoke of dying on the cross and Jesus told Peter to get thee behind me Satan. If The whole world stood up to protect Jesus from death, then God's plan for the world would have been thwarted and we wouldn't have a blood sacrifice today. Satan, being Satan, killed all the children in Moses' time and killed all the babies in Herod's day trying to kill God's seed. Why not kill all the child bearing aged women if Mary was the only woman God could use? Mary was just a girl chosen by God to fulfill His plan just as Noah, Abraham, and Moses, was used to fulfil the same plan.
Here's a note of interest. A variant of charitoo (grace) used in Ephesians 1:6 is echaritosen, in what is called in Greek grammar the " aorist indicative active." There's a sense of continuing action:
"That the glory of his grace may be praised, that which overflows upon us by his Beloved One." (Ephesians 1:6)
In a related yet contrasting way, Kecharitomene --- what Mary is called by the angel --- is a finished thing, a perfect passive participle, meaning "having been" or "have already been" graced, a past action, done to her by someone else, and fully completed in the past.
That's significant.
Here's anothr related but contrasting use of that root word charitoo: Sirach 18:17 in the LXX uses kecharitomeno. However, is not used as a form of address; indeed it is not used with reference to a particular person at all but only as a proverbial type: in other words, it is talking about a general ideal, which could be rendered this way: "the ideally grace-filled person can give both a good word and a good gift."
This is the ideal proverb-type language which the Archangel Gabriel uniquely applies to Mary as an individual, defining her (in particular) as fulfilling that ideal image.
There's another term, pleres charitoo, applied to the martyr Stephen, but it is a different term and doesn't have the specific meaning of having been perfectly grace-filled in the past. Not that Mary has grace to dispense as it were, but that she has been the (passive) recipient of a grace perfectly fulfilled.
There is only ONE time this very word, "Kecharitomene," was used as it is by the Archangel Gabriel in Luke, when it appears as a defining descriptor of one "totally grac-filled" woman, Mary --- as directly following "Chaire," which means "Hail!" which is followed by either a name, a title, or a form of address.
So the word the Archangel uses in addressing Mary, actually defining her.
Kecharitomene, a word describing a general OT "Wisdom literature" ideal in Sirach, points to only one other use: in Luke, in the NT, where the Archangel shows us that it applies to Mary individually and perfectly.
This has been discussed back-and-forth, hither-and-thither many times in the FR Religion Forum, and if you want to read the details you can google keywords
And a lot of it will show up in the google results.