Aggressive border collie
I have a female 5 yr old border collie who was attached by a german shepard in a dog park when she was 1 1/2 yr old. During the episode the german shepard was checking her out but more forceful than my dog cared for and She fought back and the dogs went at it until my dog had a grand mal siezure. Since then I've watched her carefully and the siezures are only about 1 per year when she gets overly excited. She since also doesn't like larger dogs and gets very nervous whenever she sees a larger dog.
Recently we took in a stray 9 mo female pit and are trying to find her a good home. We are fostering her because no one will take her. So far both dogs seemed to get along but recently I'm seeing more aggression from my collie. There is definitely territorial aggression and while they play well together, it can easily escalate. The pit puppy takes toys from the collie which we are trying to stop. The pit would lunge at the food but we've since made her always eat second and site first before any treat, food or chewy is given.
The problem comes when the collie out of no where will attach the pitt, biting her back and mounting her in dominance position. On walks, when we pass any dog, small or large, the collie barks, pulls and will not settle down or listen to any command. I'm forced to walk back and but her back into her crate until she settles down.
My concern is my collie's overall health, the increasing aggression, threat with the pit in the house and how she may start to imprint that aggression.
My collie is crate trained and will put herself in a time out. The pit is also being crate trained. Need help because giving up is not an option. My collie is not aggressive towards me, my children or other humans.