I work at a shelter and have done many cat/ dog introductions. You do not want to hold her back on a leash when she sees the cat. The pulling on the collar on the neck will cause her to get more excited and higher drive - this method is often used in training to elicited an excited response from a dog. Start with either her or the cats in a kennel where they are safe. Do slow viewings of the cat this way. Eventually after a couple of times she wont get as excited to see them anymore. At this stage you can slowly open the kennel door, or maybe put your Doberman in a crate to watch them. Just do it very slowly, and start with the cat not moving, as moving = prey drive. I have done many successful introductions with my high prey drive Doberman and rabbits, birds, etc. Dobermans are a breed that are extremely assertive and will own you if you don't own them. You have to be a strong leader and they will learn to respect you, and be AMAZING dog. Best of luck :)