Well, as Glenda pointed out, he didn’t actually call her ‘full of grace’ – that’s just the closest that Latin grammar could get to the corresponding Greek grammar. Instead, we have a Greek participle in the perfect tense. It expresses the notion of a completed action in the past whose effects are active in the present and are on-going into the future. In other words, it expresses the notion that God had given Mary grace in the past, and it continues to the moment he addresses her, and will continue to exist in the future.
As Catholics, we see this as meaning that Mary had been preserved from Original Sin at her conception; this grace is seen as still being in operation at the time Gabriel addressed her, and wasn’t limited to that point – she would continue in that grace throughout her life. The implication isn’t the
amount of grace, per se, but rather, the
permanence of the state of grace in which she lived…