Rescued neglected dog Annabelle needs medical diagnosis and treatment

Approximately 2 years ago I rescued a beautiful female Golden Retriever named Annabelle from a domestically violent situation, she was 6 years old and a guy I knew (going through a divorce) asked me if I could keep her for awhile until he could find her a home because he had moved into an apartment (not allowing pets) and his wife was threatening to kill Annabelle. Already having 3 dogs I said yes.. I could immediately see what a beautiful dog she was but the neglect was obvious, extremely matted/dirty fur and would react as if she was always afraid of being hit. I fell immediately in love with her and decided to remove her and not let her go back. It was when I noticed eating issues for her that I had to take her in for medical and grooming in addition too (she needed surgery on her tongue). I made the owner sign her over to me knowing she had to go to a Dr and I would be paying the bills. I have never been able to find someone I felt would be better for her than me. Over the last 2 years, I have spent so much in medical costs just to get her passed issues that were caused by the last owner taken care of and that was OK because Annabelle is such a special dog in her happiness/love she has for people. On her last dr visit, it was determined that her hips are in bad shape and recently she has started to lean to one side and fall. I figured that I may only have a few years left with her so I had her on joint meds and pain meds so I could keep her comfortable. It was an option to do more extensive diagnosis but that was way beyond what I could afford, so I went with "hope" and comfort. Annabelle is not telling me she is ready to go, her body is obviously in trouble but her happiness and mind are still strong. I am so heartbroken watching her in pain but the constant wagging of her tail and excitement she gets around people and other animals has brought me to the point of desperation that maybe somebody has a little more financial means to help save her life for awhile, get an intensive diagnosis and maybe there is something that would help her and if not then I know all options were exhausted.