How to get through the impending loss of my beloved dog

This isn’t age related, but my fellow 60+ ladies are the best source of wisdom on here. My dog has been my closest companion for 12 years and has gone everywhere with me. She suddenly started having difficulty using her legs and falling this week. We have to wait 3 weeks to see a neurologist and then get an MRI. There is nothing I can do for her in the interim other than make sure she’s not in pain and keep her safe by not allowing her to do basically anything. The emergency room vet kind of indicated that this could be the end. it’s hard to believe because she was acting like a puppy five days ago.

I don’t know how to prepare for this as I love her more than I’ve ever loved any human and I cannot bare the thought of life without her. Any ideas on how to make it through this would be great appreciated.