This behavior is not that unusual for emus, especially when raised as a single bird. A single emu often adopts one of its caregivers/owners as a pseudoparent, family member, even a potential mate! Emus, though often lovable, are not the brightest creatures in the world and when raised outside of an "emu family hierarchy environment" sometimes do not comprehend that it is not human or that its human caregiver is not another emu! We have seen birds that were raised without other flock (mob) members attempt to woo its human owner as a mate, and/or defend it's "adopted" flock member (aggressively) from other humans that it views as rivals or threats, or sometimes they just view another human as a threat/rival, just as it would behave in a natural setting when confronted with a rival emu or a predator. This can also occur with emus raised with other emus too, you may get a bird, that for whatever reason, has a "grudge" against a particular person or animal. Although no one knows exactly what goes on in an emu's mind, this does often times seems to be the case.
The only way that we have had success "breaking" an aggressive emu is to challenge it head on, which can be very exciting and potentially dangerous! Your husband would have to become the alpha emu and confront the aggressive emu during its aggression! There are a few tactics that we have had success with, the least being having a large weapon to defend yourself with, such as a tree branch or long stick. You don't want to beat the bird senseless but you do want it to learn that there can be consequences when it provokes you. Also, hold a hand over your head, as if your arm was the neck of an emu and pinch your fingers together in the shape on an emu's head. Emus will often recognize the elevated head as a much taller emu and realize that it may have chosen a larger emu to fight with and back down! Becoming the larger alpha bird and giving it a couple of whacks (only when you think there is a danger of contact from the bird) does tend to work over a period of time. The aggressive emu will never tame to the point of being "warm and cuddlely", but will give you some space after a while.