It is not the other dogs that are the problem to me. I have had herder dogs most of my life and they naturally watch your every move. She is doing her job and trying to herd you away from what she believes as possible danger.
For some reason, Your commands are being ignored, usually unknown body movements not noticed by you. They thrive on routine. Commands must have same tone each time.
They are hypersensitive to differences in their world, things most dogs never notice. We have a miniature aussie that I use to herd my waterfowl. One of my geese freaked out on a turtle and he came running because it sounded different. You can put your finger on top of your head and if never seen on a normal basis, something is wrong and she needs to investigate. My husband has this mug for coffee that he takes to work and he always sits on counter so he doesn’t forget it. One day, I put it in cupboard. He was apparently watching and noticed the cup was out of place and went to barking and pacing. Dumb me could not figure it out. He ended up actually going to dad and got him to go follow him to his problem. Dad said, whats wrong? Dog went nuts. Later that day while dog still in kitchen laying there upset, dad goes to get cup and tells me, “I want it here so I don’t get down the road without it. He places cup back and the dog settles down, touches my hubbies hand with nose and lays down. So yes, hypersensitive, and need and thrive on order. If out if order, he will tell us. Used to drive me crazy but thats not a problem with dog, it was bred into them so they can alert u long before u even realize whats wrong.
I would put her back through obedience training and also purchase a shock collar to immediately put her in her place when she is out of line in public. You won’t need to shock her as a herd dogs ears are very sensitive. We place the actual box directly under her ear not on top of back. It will only take a few times before she realizes you are alpha. As a back up in threatening situations you have the shock if you need to avoid injury/death but the lowest setting will work. Don’t shelter her away from other dogs except at home. That is her domain and she is doing her job.
Another thing to note, herders are trained opposite of a normal dog. They want to work, whether it herding an animal or you. They work better with sweet commands. To me, I would think she is even more protective of you since you rescued her from a bad situation all around. It is possible she was dumped for aggression and btw, the other mix part of her is your problem not really the border collie side.
I use click training with and after collar to reinforce good behavior. I agree with others as far as letting people know she is in training for aggression and it will take time. Slowly get her used to other dogs and show her you are ok with them being there and she will get it. Continue to expose her to dogs on a leash, let people know that she is in training for aggression and don’t worry about their feelings. This is about your dog and the time it will take for her to adjust. The “purse dog” people need to know she is super protective over you.
You are probably the first person not to give up on her and she is going to guard that situation because she doesn’t want to loose you. They are some of the most pleasing dogs out there and if given time, she will learn. I just recently rescued one about a yr and a half ago. He was a terrible mess of nerves and fear. I even had to put him on xanax for a year. Today, he is sitting to the left of hubby watching him and waiting. I am telling you, not many would have been able to handle him and would have given up. About 3-4 months ago, he finally realized he was here to stay and not all people are bad. It was a rough time but like I said, he is now my main herder and doing it well. The first 6 months we couldn’t even get him to lay down and relax. He ran nonstop all day until we went to sleep. It was crazy crazy! Loves his dad more lol but worked out fine. Herder mixes are harder to train because of the opposite brain thinking so I would work first on getting rid of one side and then work on the herder side. Good luck and hope she works out.
