You have the wrong argument completely.
Catholics are not arguing that there is a qualitative difference in the grace of God as bestowed upon the Ephesians and that which was bestowed upon Mary. The theological point being made is that
when the Annunciation occurred, the grace had already been bestowed. Why and how would Mary have been redeemed at a point in time following her conception? There is no basis to argue that she was redeemed at age 5 or age 10. We do know that before Christ was conceived, Mary was redeemed. Thank you for showing us how this verb proves the Catholic position.
bringyou.to/apologetics/a116.htm
“However, Luke 1:28 uses a special conjugated form of “charitoo.” It uses “kecharitomene,” while Ephesians 1:6 uses “echaritosen,” which is a different form of the verb “charitoo.” Echaritosen means “he graced” (bestowed grace). Echaritosen signifies a momentary action, an action brought to pass. (Blass and DeBrunner, Greek Grammar of the New Testament, p.166). Whereas, Kecharitomene, the perfect passive participle, shows a completeness with a permanent result. Kecharitomene denotes continuance of a completed action (H. W. Smyth, Greek Grammar [Cambridge: Harvard University Press, 1968], p. 108-109, sec 1852:b; also Blass and DeBrunner, p.175).”