hello everyone, i have a female yorkie called Millie and shes 2 in december. shes supposed to weigh about 5-6 pounds but is infact 8 pounds at the moment

she has begun to be abit of a pudding in recent months but im not sure why. she is constantly running around the house playing with us and my other larger dog and goes on walks alot and goes running with my fiancee' about 3 times a week.
she has a small meal in the morning for her brekfast and a slightly larger meal (abeit still small) for her tea in the evening. i live with my parents who spoil her rotten and give her tit bits all the time even though i have stressed that they cant carry on giving them to her for her health. the only "human food" meal that i allow her to have is a small (yorkie size) sunday roast (veg, meat and gravy) instead of her evening meal, only on a sunday.
i do try to make her eat healthily and make people stop giving her tit bits but as alot of you know - its easier said than done.
does anyone know any low fat wet-food avalible in the uk that would suit her?