My German shepherd is 2 years old and i want to breed her but she is quite dog agressive, mostly because she's scared of other dogs, any advice?
Please do not breed this dog.
But try this on for a plan instead of breeding your dog:
You want puppies, you want to breed your bitch. But you can see there is a problem with this one. How about if you spend the next two years learning everything there is to know about breeding and raising dogs, the German shepherd dog breed, training dogs, grooming dogs, working dogs, herding dogs, nutrition.
At the same time, work with your dog. Work to overcome her fear-aggressiveness/dog aggression. Go to lots of classes with her. Go slow, and introduce her to new things calmly and at a distance and only a few in a week's time. As the months go by increase this little by little. Train her to be awesome. Awesome in obedience, and maybe agility, and maybe herding if you can. None of this is wasted. In fact, learning how to train a dog, working with a dog with issues, training a dog in a variety of venues will help you to support your future customers.
After two years, make a plan. Make a plan to step up your training with this dog, and to set yourself into a position where you can afford and house the breeding bitch of your dreams. Decide whether you want to go with one that is full grown, or if you want to gamble on a puppy from an excellent breeder and excellent producers. Learn pedigrees and the various lines of GSDs and decide what you like best.
You have a bitch now. I would like to suggest you dedicate yourself to the bitch you have and ten years from now, you will be in a position to get your foundation bitch. Not everyone can wait that long. But, remember that having two bitches can be a royal pain, so you need to have a housing situation where you can keep the two 100% separated if necessary, and if you intend to breed then next one it WILL be necessary to separate them 100% of the time while she is pregnant and while she has puppies.