Lost my dog when I was 13 the same way.
She was a black lab/beagle mix. Katie was such a laid back dog and so easy to get along with. When I was 12 she had a ruptured disc in her back. Vet explained surgery was the only chance for a long term recovery but there was no guarantee. My parents bit the bullet and had it done. About a year later another disc ruptured. We had to put her to sleep.
My condolences!