Significance: Not a minion, not following Corypheus, but powerful in magic, a mage, Vivienne’s link to this suit for this situation of the companion quest makes sense; she does after all create a potion as a potential cure and uses a cup, a chalice.
The card itself represents: Women aged 36 and older, warmth, empathy, motherliness, home and hearth, fairness, romantic loving, insightfulness, pregnancy, being a good confidant and trusting feelings, idealism, beauty, lightness, etc.
Vivienne always did strike me as light and motherly, despite her authoritarian nature, she tends to the Inquisitor and shares what she believes is est for her or him.
Reversed: Shallowness, being self-centered, unreliable, coldness, moody, fatalistic, changeable, recrimination, anti-social feelings, poor health, being denied an all, fears of motherhood and domestic responsibilities, etc.
Dressed in a yellow gown, here representative of decay and sickness, she holds an upside down chalice, symbolic of the emptiness and loss she feels for the death of her lover. The man in the bed lies stricken and old from the disease, black showing that death has taken him, though now he is with the light of the Maker. Her neck and the shape of her collar, with her skin standing out against the yellow, shape a spade, as with the tip of a spear; one that digs deep into the earth of grounded trees to the root of magic that holds the world together. Her eyes closed in sadness, she cannot bear the look upon the darkness of the outside world, thus she faces the darkness within.
What I think this means for Vivienne: Her magic failed to save a life dear to her and she has all these views about the Circle and the Chantry, she can shed light to the understandings of magic.
What I think this means for DA: magic will not and cannot always save others, thus perhaps the darkness is inevitable in order to reach the light and perhaps a blight will bring on the path to the paradise, or more chaos will lead to more truths being uncovered. Dig up the truth, the past, History, Magic, to bring understanding.
Links to the Tarot Decks Used in the Comparison, the DAI Tarot Deck, and the Books used to determine what the cards actually represent: