Give Shadow Grace a chance

Shadow Grace is our almost 5 month old great dane baby girl. She was born April 25th, 2020 and we brought her home June 19th, 2020. Everything was wonderful and she was the best dog we have ever had. The amount of joy she brings myself and my 5 year old daughter is hard to explain. I'm sure all of the animal lovers out there know exactly what I'm talking about. A few weeks ago we noticed Shadow was not acting as a normal puppy. She was laying on her bed instead of playing and being a typical puppy. 3 weeks ago I woke up to her screaming out in pain. I thought she was whining yo go outside to go to the bathroom. I picked her off the bed and set her on the floor only to find out she could not walk. She was in a horrible amount of pain. After calling many vets offices and animal hospitals, none of which would see her, they kept telling me its just growing pains and I needed to ride it out. I went the weekend and things progressively got worse. I called her primary vet and begged them to see her. They agreed and away we went. After blood work and testing for Lymes disease they still strongly believed this was just growing pains. They gave her steroid shots and pain meds and sent us home. After 2 days she started walking. I thought we were going to make progress. She walked for a total of 2 days and went right back to not being able to walk and being in pain. Her joints were so swollen, on every leg. I took her back to the vet and after more bloodwork they figured out she had septicemia, a blood infection.  So we started the antibiotic on Sept 8th. And they also put her on another pain med to hopefully control her pain. Today things have taken a turn for the worse. She cannot walk at all. Her legs and joints are so swollen, almost 3 times the size they should be. She is only getting worse. Shadows primary vet and myself have been on the phone with Cornell animal hospital all afternoon. They are pretty sure they know what is wrong with her but in order to diagnose her with what they think is a form of cancer, it will cost anywhere between 2500 and 5000 dollars. We are left here with two options.... ask for help from our friends and family to get Shadow a diagnosis or we are left with the decision to put her down. We cannot stand to see her in pain any longer and we are absolutely heart broken. This is our girl. We are at a loss and not quite sure what to do. Anything helps, even a listening ear at this point. Thank you so much everyone.