i have a female japanese spitz 1yo (she is 6 kg). i notice that recently she is getting increasingly aggressive towards puppies that are smaller in size than her. The incidents usually happen when she encounters a puppy and either 1, the two sniff each other's face/mouth or 2, the small puppy licks her face, then she would suddenly lunges forward at the puppy and/or try to snap the puppy. i notice that everytime she encounters a small puppy, her posture is tense with some tail waggings in small movement.
She is very submissive (lies still and shows her belly) towards older dogs or puppy of larger size (e.g a husky).
Has anyone encounter a similar situation? is this a dominant behaviour thing?