What do I do about my aggressive dog.

[AussieLove]

My family has a 9 year old Golden Retriever. I moved out of my mothers house in January of this year with my husband. As a valentines day gift he bought me an Australian Shepherd to be trained to be my service dog. (For those who are curious I have panic disorder and can't be alone/in a crowd/in stressful moment by myself etc.) He is will be 11 weeks on Wednesday. I go to my mothers house everyday and didn't change that when I got the puppy. When we first got him at 6 weeks she was terrified of him, we assume because he was so small. She has a safe place behind the couch that she goes to whenever she is scared, or really whenever she wants to. He wasn't very energetic when we first got him so we thought it was because she was afraid she was going to hurt him. After about a week or so she started to growl and show her teeth at him. We would smack her on the nose and tell her no, she would snap at him a couple of times (over food or toys) not full on attack but you know snap at him. As the weeks went on and he started to get a little bigger and more energetic she began to get more comfortable around him. She would play with him even doing the showing teeth but slowly and softy play biting him. We thought all was well. I began training him with treats and was using her to show him what he needed to do. (This was about 2 weeks ago) He got a little to close for comfort when I had a treat in front of her face and she attacked him. She didn't hurt him, no blood, mainly just scared him. I knew it was my fault because of the treat so I decided neither of them would get treats while they were together and I would do his training separately at my house. He seemed weary of her but still played with her when she showed she was ok with it. She seemed to be fine since we had taken away toys, food, and treats. (They would get them only when they were separated.) She was doing great until tonight. They played together in the house, my sister and I took them both on a walk (Note she never shows aggression outside of the house), they very much enjoyed themselves. We decided to go get food, we locked up the puppy in the cage to separate them then left. We were gone for maybe an hour, when we came back we let the puppy out of his cage and he went straight to the water bowl. The Golden Retriever was in the kitchen. He has done this numerous times in the past. They have drunk from the same water bowl at the same time and had no problems whatsoever with that. But tonight she wasn't even drinking out of the water bowl. He bent his head down and she grabbed his leg. My sister was in the room and pulled her by her hind legs off of him, she stretched out and grabbed his head. I got to her and pulled her by her extra fur and she pulled him with her. She wouldn't let go until I put her in a choke hold. He has 5 marks (that I can find, every time I look I find another). Two on his leg where she initially grabbed him (top and bottom) and three on his left face (One on his cheek, one right before the ear, and one right on the ear where it connects to the head). I don't know what to do anymore. We've taken away anything that could cause aggression and yet she still attacked him for no reason. Her attacks are getting worse and seemingly more hateful. He's so small compared to her I'm afraid the next time she'll severely hurt him or worse. She was attacked as a puppy by another dog that was walking outside while she was on a walk so she's always been scared of other dogs but she was fine with my grandma's puppy and my cousin's smaller dog (who was already 2-3 when she met him) My puppy is the same size now as my cousin's dog. We thought it was a size issue, or age issue, but now we have no clue what's wrong. I can't get rid of either of them, he's being trained to be my service dog and she's a family dog that we've had ever since she was 6 weeks old. I can't not bring him to my mom's as I live 30 minutes away and he needs to be with me as often as he can and I can't stop coming over to my mom's house. We have no idea what to do, my husband in the immediate anger after hearing about this incident (he wasn't home and I called him immediately after it happened) said the next time she does this he's getting her put down. None of us want that, we love her and don't want to end her life because she can't handle having a puppy in the house. What can we do to make them get along, or at least tolerate each other?