The toy was on loan by local aristocrat Sir Benjamin Slade and was disemboweled of her some of her stuffing and had her head bitten in the attack.
The rare toy, made in 1909 by German manufacturer Steiff, was valued at more than A$100,000.
Mabel was to have formed the centrepiece of a valuable collection on display at Wookey Hole Caves in Somerset in south-west England.
However the bear upset Barney, the Doberman pinscher charged with protecting Mabel and other fluffy exhibits, and the dog launched into a frenzied attack.