It is not only permissible but highly advisable. The saints have engaged in this practice, and the Holy Scripture even mentions that angels carry our prayers to the throne of God. During the Holy Mass, the Church explicitly invites the angels to join us in singing the Sanctus. They are active participants in our prayers during every Holy Mass.
In your private prayers, it would be wonderful to invite your guardian angel to accompany you and join you in prayer. The example from Fatima, where the angel of Fatima prayed with the children, “My God, I believe, I adore”, is a beautiful illustration of this practice.
Dear visitors of Gloria Dei and all who have already written or who will write a personal message to me. I am grateful for your attention, your kindness, for your spiritual support and especially for your sacrifices and prayers for me. God may reward you!