My Father has stomach cancer and over Christmas was vomitting excessive amounts, we assumed it was the chemo that he had had. None of the anti-sickness drugs were working when he was in Hospital and a scan was carried out which showed his stomach was completely blocked. Not saying this would be your Nans problem but its worth investigating. My Fathers tumor is of the aggressive type, also all his contents of his stomach were being brought up after eating. He now has as stent , which lets him eat small amount of mashed food.
Good Luck
Gail