Mary, if the Son is part of this eternal procession of the Holy Spirit from one principle then logically that principle cannot particularly be the Father.
The principle of the Father is one way to look at the so-called procession of the Holy Spirit. The other way is to look at the Trinity as principle in the so-called procession of the Holy Spirit.
In the east, the focus has traditionally been on the Father-As-Principle.
In the west, the focus, in part because of language and in part because of the Arian heresy, has traditionally been on the Trinity-As-Principle.
As far as I am concerned, neither is wrong, and taken together the image of the Trinity in essence and in economy becomes most complete.
I have something archived from Apotheoun which points to the error of the procession from the Trinity As Principle.
"Texts which speak of the Son having "all things" in common with the Father, or which speak of the Spirit as having "all things" in common with the Father and the Son, concerns the consubstantial communion of the three divine hypostaseis, and not their manner of origin (tropos hyparxeos). To deny this distinction is to fall into the heresy of Sabellius, who confused the distinct hypostatic properties of the Father, Son, and Holy Spirit, with their common essence. The Son and Spirit receive their hypostatic existence from the Father alone, because He is the sole cause, principle, source, and font of divinity; and so, by generating the Son and spirating the Holy Spirit, He (the Father) imparts His own essential nature to them.
"In order to understand these triadological distinctions better, and to see why the East rejects the filioque
as defined by Florence and Lyons II as heretical, I recommend reading the recently published dissertation of A. Edward Siecienski, which is entitled, "The Use of Maximus the Confessor's Writing on the Filioque
at the Council of Ferrara-Florence (1438-439)."