Why does my Coton take a mouthful of food and go roll in it? How do I stop this?

Sushi is 13, she and I have been together since she was 6. She is in reasonable health although due to a gum disease no longer has any teeth. She also has as the vet put it, an intolerance to all foods, bar sweet potato and egg... anyway long story short, I have researched her condition and now make her a page of chicken livers rice and sweet potato in addition to the dry diet recommended by the vet. The problem is, she takes lumps of the pate in her mouth, then throws it on the carpet and rolls in it. If I’m not quick enough to stop her from doing it... well you can imagine the carnage afterwards. Any tips or advice, gratefully received, thank you. Kirsty, Brighton, UK