Sorry this is long. I'm struggling to figure out what to do with the newest addition to our family, a 15 month 7 lb yorkie, Bella, that joined our family 3 weeks ago. I have 3 other older dogs and for the first week, all was well except for a few small spats easily resolved. She is very sweet to us and very loving, the problem is how she is with our other dogs. A couple of times one of my older dogs, Noel, growled at Bella when she tried to jump up near her. That began our main issue. Now for 2 weeks every time Bella sees Noel she starts growling and runs and lunges at her. We have separated them and tried to only have them in the same area for short periods of time while they are both being fed treats to keep Bella calm...Noel is calm just scared of her. We have tried to walk them together but Noel (20 lbs 7 yrs) is scared of Bella and avoids her while Bella struggles so hard to get at her she won't walk, first growling and barking, then whining. I have dealt with multi dog aggression in the past but I am struggling to deal with the situation where the aggression is held on for weeks. When Bella has the same situations with our other 2 ( random growing/spats) they would get over them and move on but with Noel, if she even catches sight of her she tenses up and starts to growl. As for Noel, she will stare and watch Bella from a distance or turn her head and not look at her and if she is near she will tuck her tail between her legs and hide. I have tried keeping Bella on a leash with me and whenever she showed aggression toward Noel I say shh/ quiet and wait until she calms down then we move on. She is also given treats when she sees Noel. She does calm down after a little but it's been 2 weeks of this. We have had to buy and put up gates to keep them separated in the house. Now, yesterday, she is trying to attack all the dogs through the gate so I'm worried it is having the opposite effect on them...creating aggression. Also, a problem she has with the other dogs is if they do a small warning growl to back off she goes from 0 to 100 and decides to lunge and attack them immediately. She over reacts. I have researched for 2 weeks, implemented different training strategies, tried all sorts of things but it's not getting better. I know it has only been 2 weeks but it's worse! I am a stay at home mom with 4 older kids and we are all working on this but I am concerned it will not get better and I am nervous of a future where we are constantly on guard making sure they are not attacking through the gate or if Bella gets out. I do let Bella and 2 of my other dogs play in our yard together. Generally, all goes well unless I sit down and they all want to sit with me (Bella stares at other dogs and lunges) so I don't sit. In the house Bella can also start random fights with the dogs. Do you have any advice? Has anyone who has been through this before had it work out! Is there hope?