Willow used to hate cats, but when Buffy came as a 4 week old orphan, Willow took her under her wing (they were playing together in just a couple of weeks). Willow used to be terrified of my dog, Jake. Whenever he came into view, she would shrink down wherever she was and hope he didn't see her. If he did see her and chased her, she would just run away. But when Buffy came, she stood her ground a little more. One day Jake, Buffy, and Willow were with me and my sister in my parent's room. Buffy was on the clothes shelf thing, Willow was under the bed, and me and Jake were on the bed. Eventually my sister decided to bring Buffy to the room next door, my room. So she reaches up for Buffy, Jake immediately sits straight up and stares (he's a Border Collie/Australian Shepherd mix) and Buffy squawked, as she always does when someone tries to pick her up when Jake is around. My sister then takes her around the corner to my room, and when she disappears, Jake jumped off the bed and started scrabbling for her. I was holding onto his leash so he was just slipping and sliding, panting and wheezing ("C'mon, lemme at her! Lemme at her!"). As I got to the corner where we turn, I felt this wierd warmth on the back of my legs, then pain, and then heard a shrilly cat siren meow. I look back, and Willow is standing at the doorway of my parent's room, puffed up, side facing us, and growling. Jake doesn't even notice her, he's so intent on watching what my sister was doing with Buffy (putting her on the bed). So then Willow comes forward again, starts lashing at my legs and Jake's legs and then backed off to the doorway of my parent's room again. Again Jake didn't even acknowledge her existance, he just kept staring. So she runs forward again and kind of races up alongside Jake, using his side as a scratching post (you know, using it to sort of pull herself forward?). Now she was standing and snarling at the other end of the hall and this time Jake had noticed her. So they're doing a little stand off, Willow warbling and meowing, Jake just staring in interest, my sister finally coming to see what the screams (human) were about. As my sister got to the doorway, Willow ran forward again and latched onto Jake's face like velcro. Jake, in turn, lunged forward and shoved his face into Willow's belly. So they're scrabbling around like that, Willow refusing to let go of Jake's face, me and my sister screaming at Willow to "GET OFF!!" (normally we'd be telling Jake to back off instead). Eventually Willow lets go of Jake and runs off back down to the end of the hallway, where she starts growling again. My sister runs after her and chases her down the stairs, so she can shut the door and keep her from attacking Jake again. When I checked Jake, his muzzle was gushing blood. It looked worse than it was, actually, the bleeding stopped in 5 minutes. But then Jake saw Willow standing on the other side of the door (it's made of glass and wood, so you can see to the other side). So Jake naturally charges at the door, growling and snarling and just being overall frightening. Willow, on the other side, just sits up straight and screamed back. I swear, it was like two teenage siblings screaming and cussing at each other, but this was scarier. So I took Jake outside and we brought Buffy (who acted oblivious to the whole thing) downstairs so Willow could check her over. That was over a year ago, but I still have scars on the backs of my legs, lol
Willow then attacked Jake 3 more times in other incidents, but this time we got more warnings. She would step in front of Buffy (one time she looked like she was cradling Buffy between her legs) and then we had to get Jake out of there or else she would drop down and latch onto him again. It took 3 times before we got the message and started taking him away. She now attacks him more often, but not to the level as the first 3 or 4 incidents. This time she'll sort of run at him, hop up and down on his back, and then run off. The other day she bolted outside so I brought Jake out to help me round her up (she always loses her composure when he comes around, so she doesn't feel like having fun anymore). Well, this time I think she started to understand I would never let Jake hurt her, so she got bold. Now when she started to run from me, I would have Jake go after her (for him to go around in front of her, to stop her running). Well, as soon as he got alongside her, she stopped, dashed at him, swatted, spat, and then took off again. So it was like that until I finally managed to corner her and catch her myself.