Advice After a Dog Bite

My girlfriend's Australian Shepherd recently bit her after a smoke alarm went off. He latched onto her arm and bit 3 times, enough to break skin and need medical attention. He is over 60lbs and I had to pull him off of her to get him to stop.

Now we're facing a difficult situation. She's had him his whole life (about 8 years) and is strongly against euthanizing him or putting him in a kill shelter, but I've contacted over 50 rescues and farms and nobody will consider him with his bite history.

I do not think training and keeping him is on the table. Because of his size, if there were ever another attack when I was not around I'm afraid he could seriously injure her or worse.

I've contacted every Australian Shepherd related shelter or rescue to no avail. I'm afraid that we may end up needing to put him down. Do you have any advice on possible next steps or guidance? We both feel pretty lost right now.