There is nothing in the homily that contradicts the fullness of grace given Our Lady.
Pope John Paul II:
Mary was granted power to resist the devil
2. The same biblical text also proclaims the enmity between the woman and her offspring on the one hand, and the serpent and his offspring on the other. This is a hostility expressly established by God, which has a unique importance, if we consider the problem of the Virgin’s personal holiness. In order to be the irreconcilable enemy of the serpent and his offspring, Mary had to be free from all power of sin, and to be so from the first moment of her existence.
In this regard, the Encyclical Fulgens corona, published by Pope Pius XII in 1953 to commemorate the centenary of the definition of the dogma of the Immaculate Conception, reasons thus: “If at a given moment the Blessed Virgin Mary had been left without divine grace, because she was defiled at her conception by the hereditary stain of sin, between her and the serpent there would no longer have been—at least during this period of time, however brief—that eternal enmity spoken of in the earliest tradition up to the definition of the Immaculate Conception, but rather a certain enslavement” (AAS 45 [1953], 579).
The absolute hostility put between the woman and the devil thus demands in Mary the Immaculate Conception, that is, a total absence of sin, from the very beginning of her life. The Son of Mary won the definitive victory over Satan and enabled his Mother to receive its benefits in advance by preserving her from sin. As a result, the Son granted her the power to resist the devil, thus achieving in the mystery of the Immaculate Conception the most notable effect of his redeeming work.
3. By drawing our attention to Mary’s special holiness and her complete removal from Satan’s influence, the title “full of grace” and the Protoevangelium enable us to perceive, in the unique privilege the Lord granted to Mary, the beginning of a new order which is the result of friendship with God and which, as a consequence, entails a profound enmity between the serpent and men.
http://www.ewtn.com/library/papaldoc/jp2bvm21.htm