I adopted a 3 year old Aussie in November. She seemed to have a reasonable temperament initially. (At home, she's a lap dog).

A few weeks after I adopted her, I realized she was pregnant. She had 7 puppies 3 days later, only 3 of which survived.

Since the birth of the puppies, I noticed aggressive behavior in Katy. She growls deep in her chest and barks at people who we encounter in my apartment complex. She's especially aggressive with other dogs. She's actually gotten away from me twice, and she doesn't do anything when she gets to the object of her attention. She sniffs and follows, but she doesn't jump up on or bite.

The puppies are 8 weeks old, and are nearly completely weaned. Lately I have been taking her and the pups out at the same time and letting them play and potty all at once. Katy's been really great, and though there would be some barking, she'd come when I called her and I could get a leash back on her before anything could upset her.

Today I took Katy outside and when she encountered another dog, they both errupted into very aggressive barking and pulling. I took Katy back inside to calm down, but since then her behavior has gone back to what I'd initially noticed. This evening, she actually pulled me off of my feet and i fell on the concrete (I am 5'8" and by no means a small woman) so that she could go after some young men who walked through the complex. One of the boys actually screamed, believing he was about to be mauled. As usual, once she got to him, she just sniffed him, but I'm worried that her behavior could cause trouble. I don't want to scare my neighbors. I don't want to be pulled off my feet.

What can I do to correct this behavior in Katy?

(PS: I never intended to have a dog her size in an apartment, let alone 3 puppies. I'm in the process of buying a house on a half acre).