What Breed Was My Dog?

She was rescued from some travelers who had a lot of dogs. We took her to the vet, got her shots, and they said she was a Jack Russell mix, but we want to know what the "mix" part is. She was the only ginger in the litter and neither the travelers or the vet knew anything of the father. Her mother was the Jack Russell. She was a bouncy, loving dog with a passion for chasing rabbits. Any ideas?

P.S. If it helps she lived to 14 yrs old