Didn’t Mary’s consent occur before she conceived by the Holy Spirit? But in the Angelus prayer “She conceived of the Holy Spirit” comes before “Be it done unto me according to thy word…” Shouldn’t the order be the other way around?

Some theologians argue that Mary conceived in her heart before she conceived in her womb. Though this is not likely what is meant in the first strophe of the Angelus prayer.
 
More specifically, liturgical prayer accesses chronological time with reference to the fullness of time. Thus at Christmas, though referencing Jesus’ infancy, we still gather with him in the upper room, and at the foot of the Cross, and celebrate him as risen, glorified Lord, at Christmas Mass. Though we focus on one aspect of his temporal work, we always have the whole in mind. Content and context trump chronology.
 
The same can be said for the Angelus prayer. We are not simply declaring the event of the Incarnation in a strict, chronological way, but in a way that theologically expresses all the components understood wholly: God’s initiative, Mary’s assent, and the fact of the Word becoming flesh.