The Church, in her wisdom, understands the heart of Mary in light of Isaiah 61.
Mary is conscious of the direct action of God in her heart.
The first image used is clothing:
He has clothed me in the garments of salvation … like a bride adorned in her jewels.
God, it seems, has been on a ‘shopping spree,’ indulging Mary with garments of extraordinary beauty and jewels of great value.
The second image used is gardening. Just as a ‘garden makes seeds spring up,’ so Mary is full of integrity and praise.
Hence, Mary’s deep joy.