Help me! Ellie is biting us!

[Lahree]

I can somewhat understand her biting and having a fit when we leave, but I cannot figure out why she bites us when we come back in! She especially gets wound up when we go out, get the mail and come right back in. That's when she is waiting right inside the door and immediately jumps up and bites and makes an aggressive snarling/growling/bark as she is doing it. The other two Shelties I had never, ever did anything like this, so I am completely stumped. Ellie is a very willful little girl. I get so frustrated sometimes that I could just pull out my hair.

 

[Caro]

Deska would do that too - so darn exciting when I come back he gets a bit of referred aggression, nipping and barking (even if its only for a couple of minutes) - except he now has a squeak toy shoved in his mouth when I come in the door and it really helps.