What is this creature?

This foul beast has been living with us for 16 (wonderful) years. She apparently came from a litter of Miniature Jack Russels (which is where her tail was docked). Loyal to a fault, incredibly intelligent and still very active in her old age. No idea what she is, so any help would be wonderful. I’ve attached a couple of photos of her over the years, most recent first. She’s around 40cm tall and 60cm long, I can’t get an accurate measurement because she thinks it’s a game and runs away. Cheers!