Help! Aggression issue...

[perdy]

Due to some personal misfortune my dog, Saturn, and I have had to move home with my mother. She has two Shih Tzus, one male and one female, age 6 and 7. Saturn is a Corgi/German Shepherd mix, female, age 6 and about 3 times or so bigger than my mother's dogs. None of the dogs have been fixed either. Saturn hasn't really been around other dogs since she was about 1 and a half, until a week ago.

When we first got here Saturn and the male seemed to get along fine. Saturn would get a bit grumpy with him at times because she was in heat and tired of having her lady parts sniffed but she didn't display any signs of aggression with him.

The female Shih Tzu is a different story. She is very protective of my mother and Saturn is very protective of me. She growls at Saturn often and has provoked her into scuffling (minor incidents that were quickly extinguished). However, tonight Saturn and her got into a pretty serious scuffle (Saturn had her by the neck and was shaking her a bit, no blood was drawn though). We were not sure who instigated that incident.

My question is: What can we do to remedy this situation? A lot of the articles that I have found have to do with puppies. Both dogs are very sweet, just not to each other. I am also a bit concerned that with my dog being part German Shepherd that this may become something bigger than it is at this point. I didn't raise my dog to act that way and it really scared me to see that happen. Any advice or other words of wisdom would be greatly appreciated.