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1) I don't know.
2) Daughter of Earth applies a random curse to the enemy when she attacks. If the curse is a slow effect, the enemy will not counterattack.
As far as I remember, and will remember in the future, a slowed enemy will not counterattack the Daughters of Earth.
3) Only if there is a second Orc castle or a neutral building where spells can be learned (I haven't encountered it on my favorite maps yet, but it seems to exist).