It is more than being apart of Tradition, is is also Scriptural.
In Luke 1:28, Gabriel used a Greek work as a Title, that word is Kecharitomene, commonly translated as “Full of Grace”, which is really an incomplete way of conveying what Gabriel was saying. Some editions translate that as “highly favored one” which is even less complete.
If you look at the Greek itself, it uses the root charitoo (Grace). It is is the past participle, perfect tense, passive voice form of the word.
What that means, in this one word, is that Mary was fully and completely endowed with Grace in the past, that she did not endow herself, but it was done to her, and that this complete fullness of Grace contintues to the present.
Oh yea, Gabriel also used this, not as an adjective to describe Mary, but as her title. As far as Gabriel was concerned “Full of Grace” was WHO Mary was.
Here is a bit more.
bringyou.to/apologetics/a116.htm