Grief after dog passed away.

I recently lost my 13 year old German Shepherd mix. She is my first dog. My trusted companion and more like my child. She was with me when both my grandparents died and when I had a stillbirtth. I am lost without her. I feel myself falling into a deep depression and am looking to find some answers that can hopefully bring me some peace. About 3 months ago, Gabby started having serve problems with her hind legs. To the point where she could barely walk. I took her to 3 different vets and ended up at a neurologist. The neurologist put her on gabapentin, tramadol and rymadil. Gabby was doing better. Then about a week before she passed away, I noticed her walking was getting a bit worse again. I also noticed her gums were pale sometimes. And she was having diarrhea. I took her to the vet who took her off the rymadil and I made an appointment with the neurologist again. When I took her to the neurologist her heart rate was very rapid. 240 bpm. She said this was concerning and did a chest x ray which showed that Gabby had pneumonia. The vet said the rymadil had probably made her aspirate. They hospitilaized Gabby and put her on a strong antibiotic and were doing nebulizer treatments. She seemed to be doing better. After about 48 hours at the vet, they phoned me and said things had taken a horrible turn for the worse and Gabby had developed ARDS. They had placed her on a ventilator. I rushed to the vet and after talking with numerous vets had her taken off the ventilator and put in an oxygen chamber. We did this for about an hour and tried other medications and then it just became too much and Gabby passed away. I am heart broken. I cannot function. I am crying non stop. I am not leaving the house. I am lost without my dog. I feel like I killed her. Should I have noticed signs that something was wrong earlier? Should I have known to not put her on Rymadil? Should I have left her on the ventilator? Gabby made me a better person. Calm. Loving. Giving. She put me at peace. I always wanted to do right by her and feel like I failed her when she needed me most. How was I unable to save my dog. Did I miss something big? Should I have taken another course of action or did I do everything I could? I can't bring her back and it's tearing me up.

Hi Dr. Marie- thank you for your response.

The vet definitely said she had aspiration pneumonia and that it was from the Rimadyl. Her chest X-rays showed pneumonia but it doesn't add up to me either.

She was fine on Friday. Well not 100% but she was ok the gone Sunday night. I don't understand and feel like there must have been something I could have done or missed.

Degenerative myelopathy can cause this?