Good question. Most new drug candidates or dietary interventions are difficult, expensive or potentially harmful, so prior to testing in people, researchers want to be sure they are safe and effective, which is why they test first in animals. Mice are not little people, but are more like humans than simpler model organisms, such as flies, worms, and yeast. Of course there are many individual factors that can alter the risk for each person. I'm very sorry to hear about your mum--that must have been very difficult.