My 2 year old northern inuit is getting quite aggressive when she is on the lead. This has been happening since she was speyed 12 months ago (maybe just coincidence) She likes all the dogs she has known since she was a pup and some of the new ones,the others are a real problem. I have her on a head collar , I think I am making things worse now as I start to dread passing dogs we dont know. Any advice would be welcome.