Best form of training/reinforcement for an animal:

My husband and I just got a dog yesterday from his old neighbor. His neighbor couldn’t take care of her, so his neighbor’s son was fixing to put her in a shelter. We decided to take her in.

She has 7 weeks before her baby sister gets here- and we’re trying to teach her not to be so possessive with food. She tries to attack the other dogs when they eat her treats (she is a grazer and won’t eat all at once). She doesn’t mind very well, although we’re currently trying to train her. My biggest problem is getting her away from her possessive behavior with food, as she gets aggressive. I was wondering what your thoughts were, CC, on the best way to train a dog/reinforce their behavior.

Are some methods harmful? Can some hurt more than they help? What do you believe is the best?

A picture of when we went to pick her up :)