Ava is 15 weeks, since got her at 10 weeks she has been around lots of other dogs, on walks, at dog friendly restaurants, and has been to the dog park a couple times. For the most part she likes other dogs and plays well with them but on two occasions now she has not. The first time we went on a walk with some friends who have an adult Doberman who basically ignored he, but Ava insisted on hacking and acting very scared of him and wouldn't go near him. Then our neighbors were letting their dog outside and we were outside too and Ava started growling and hackling at them. She was NOT happy about them being outside the same time as us. She hasn't been formally introduced to that dog yet but I'm concerned. We start puppy school in a few weeks and I don't want her to be scared of other dogs, considering she's met and been around many so far. How do I handle this?