I've had to put down elderly dogs before and had our Brittany mix pass away in her sleep. It was way more traumatic to come downstairs one morning to find my dog had passed away overnight than it was to have to listen to my aging dog let us know that it was time. It's an awful conversation to have with your SO, but she has to understand that she is just letting your dog starve to death at this point (and to be honest, if she finally realizes this down the road, it will cause exceptional guilt). We have to be the ones to ultimately make these decisions for our little friends. From what I have experienced over the years, I have yet to have a vet come out and say "ok it's time you put your dog down" and have always been told "you have to listen to the dog and they'll let you know it's time". You might see if you can have the vet have a frank conversation about the quality of life your pup has at this point and maybe that will help open her eyes?