You have gotten great suggestions. Bailey had this same problem before obedience, and still barks like mad when big dogs come toward him, but if we walk toward them or if I tell him to sit, then he does ok. My only addition would be to keep Heidi on a leash once you walk down the block to your house and inside. If any aggression pops up once you are at home, you have "control" of her..at least to the point of being to get her away from the situation.