spots on the nose is called a butterfly nose, and it does not mean that the dog has too much merle in her. i would breed her to a dog with a strong history of black (or liver for reds) noses. if you really want her nose to go black, and you don't think it will on it's on, feed her dried kelp everyday. read your breed standard before you breed (and don't breed until you know it by heart) the akc australian shepherd breed stanard says "Nose--Blue merles and blacks have black pigmentation on the nose (and lips). Red merles and reds have liver (brown) pigmentation on the nose (and lips). On the merles it is permissible to have small pink spots; however, they should not exceed 25% of the nose on dogs over one year of age, which is a serious fault."
hope this helps! Leah