How about a little well-timed bribery? Don’t feed her before you let her out and hope that hunger and delicious dog food and/or treats does the trick when you want her to come back in.
However, that’s not the only part of the problem. The fact that she growls and gets nasty with you is a serious problem which won’t just magically clear up on it’s own. The next step could very well be a bite if she doesn’t get straightened out about who is the alpha (that should be YOU) in this relationship.
A good round of general obedience training consistently applied should correct that. Either find a good trainer if you are reluctant to tackle it yourself and can afford it or get a good book written by someone with a good reputation.
The Monks of New Skete have an excellent reputation and sell both tapes and books on how to train your dog. They raise and train superior German Shepherds and this is in large part how they fund their order. They also accept clients from the general public who wish to train their dogs. . They are located in upstate New York if I remember correctly. There was a short-lived series on APL a few yrs. ago that portrayed their working with the dogs and their philosophy of training. I was sorry to see it go off the air. I thought it was terrific.
There is also Brian Kilcommons (sp?) who has excellent books and also a forum on his web page for folks to participate. He is also in upstate N.Y.. He was a protege of Barbara Woodhouse (the British lady who sounded sort of like Julia Child and popularized the term “Walkies”) She was well known for her “no bad dogs” philosophy-a very positive approach which he has also adopted. Her book would also be good.
Another guy who impressed me was Matthew Margolis who had a series on PBS for a couple of seasons. He also has a website with a section about the pros and cons of training your own dog. There is also a really good section about dealing with aggression and identifying causes.
He is in Calif. and also has a dog training facility.
Here’s the link
http://www.unclematty.com/training/dangerdogs.htm
If you don’t do something about her defiance of you, it will get worse, so you should really nip it in the bud asap. I have purposely not included Cesar Milan as his methods are pretty controversial and of the “don’t try this at home ” variety. The others I have listed all have a very loving and positive attitude and methods.