I know how you feel, MyIrishWolfie. I adopted a dog from a shelter about a year and a half ago and we too had her only two months before we had to return her to the shelter. (We named her Minnie). She was going after Daisy. She actually caused my Daisy to need a bunch of stitches in her ear because she ripped it! Daisy was miserable with that dog, and we couldn't keep her any longer. She did go to a rescue through the shelter, though. We were very upset to give her up, I even spent $400 on a trainer. Minnie was a very dominant dog and needed to be the only dog. We would have worked with her counter surfing, on-leash dog agression, and other issues, but we had to think of Daisy. She was terrified of Minnie. If Binn is miserable with Stella around, it might be best to rehome her. Keep in mind that it will take a loong time to do so. It takes a looong time to rehome large dogs with NO issues! Best of luck to you!