Mouth ulcers

Please can anyone recommend something for my mum. The chemo she's on is causing seriously large, blistering mouth ulcers on the inside of her mouth, cheeks, back of her throat & the surface of her tongue. She's is really struggling to eat, drink, swallow & talk. She has tried numbing gels, ulcers creams & liquids etc. 
Any advice would be much appreciated. 
Thanks