Our Lady still needed the sacraments because She was still subject to the Old Law (i.e. purification) and also the Church, post Pentecost. The protestants reduce everything to grace/sin, which is an error. Our Lady needed the sacraments because of Church AUTHORITY (i.e. baptism is required for salvation and so is the Eucharist, for adults). This is the part that protestants want to ignore - that Christ created the Church with RULES and even Our Lady needed a Savior (so She says in the Magnificat), even if She didn't need a Redeemer (because She didn't have original sin).
This is not exactly true. We have to understand the nature of Adam/Eve, pre-sin. They were not tempted to lust, or envy, or hate, or any sins related to our fallen nature. They were only tempted by PRIDE, (similar to the angels) because Adam/Eve's nature was in a perfect state. Lust, envy, hate, etc are sins whereby the emotions/will rebel against the intellect. But this was not possible for Adam/Eve because their intellect/reason was IN CONTROL of all their human faculties. The only way for them to sin was through their intellect/reason, which we call pride.
In the same way, Our Lady could not sin by way of her lower nature, because Her lower nature was not corrupted. Therefore satan wouldn't tempt Her in this area; it was off-limits to hell to tempt Our Lady, which is why She is so unique and holy. And because the only way She could've sinned was through pride (i.e. intellect/reason), and She didn't, this is why the devils hate Her so much, because She is literally, the most-humble person who has ever lived (and the most humble of all creatures COMBINED) because not once did She ever sin through pride, but her humility was constant, perfect and pleasing to God in every way.
So, yes, in theory Our Lady could've sinned ONLY through pride (but She did not). But it's incorrect to say that She was tempted to impurity or anger, etc. Neither was Our Lord tempted to any of these sins, because His passions were ordered and controlled (just like Our Lady's) by reason, as God originally designed Adam/Eve.
What you say makes sense. I don't have any doubts about the dogma, but I would like some clarifications about the cardinal sins.
I understand that lust is something the body would feel, or that gluttony is something the body would feel, therefore a human before the original sin would not sin through those. For sloth, similarly, I imagine that is a problem caused by a disordered relationship between the body and will. I can easily imagine that an angel wouldn't feel slothful, since they do not have a body, it would be absurd.
However, is that really the case for envy, wrath, and greed? As an example, I think that Adam/Eve didn't merely sin through pride (putting themselves before God), but they also envied God's knowledge of good and evil. Even the most unparalleled intellect of the universe would feel inferior to God, and for someone who values intelligence above all, I can easily imagine wanting God's intellect. For greed, refusing to share wordly possessions with others would be an example, and I do not see how it is related to the imperfect state of the body. For wrath, I'm not sure either. It seems to me even someone with perfect intellect could wish harm on others.
Again, about the sin of envy, imagine as an example if our Mother had the thought that she didn't want her son to suffer to such an extent, and would prefer if it were anyone else instead. Of course I think she didn't have the thought (since the Church teachings say so), but was such a thing possible in theory ?