She asks her Guardian Angel to "defend me against all the assaults of my enemies."
St. Gertrude the Great was a holy mystic of the 14th century. She began receiving heavenly visions at age 25 while living in a Benedictine community. She is probably best known today for her visions of purgatory and the Sacred Heart of Jesus.
In her writings she also composed a special prayer to one’s Guardian Angel. It reflects her own spirituality, especially her devotion to the Sacred Heart. She also invokes the powerful spiritual protection of her Guardian Angel, asking him to “defend me against all the assaults of my enemies.“
If you are looking for an alternative to the traditional “Angel of God” prayer, here is St. Gertrude’s version.
O most holy angel of God, appointed by God to be my guardian, I give you thanks for all the benefits which you have ever bestowed on me in body and in soul. I praise and glorify you that you condescended to assist me with such patient fidelity, and to defend me against all the assaults of my enemies. Blessed be the hour in which you were assigned me for my guardian, my defender and my patron. In acknowledgement and return for all your loving ministries to me, I offer you the infinitely precious and noble heart of Jesus, and firmly purpose to obey you henceforward, and most faithfully to serve my God. Amen.