Ms Griese had her takings from both events stolen at the end of the Smithfield event at Shepton Mallet.
In total about £1700 was stolen, £800 of which was cash and £1100 in the form of cheques.
“A friend suggested if people knew of this they would stop the cheque and write me another one,” she said.
Mary Griese has gained international renown for her watercolour paintings of livestock and domestic animals.
The cheques were written out in her name although her business is called Slightly Sheepish.
To contact Mary call 01275 472207.