Why is this in spoiler tag? I thought book spoilers were cool in here? Anyways, I have a feeling D&D found the "valonquar" resolution in the books, as revealed to them by GRRM, to be cheesy or maybe Maggy was completely wrong and no valonquar of any kind plays a role in Cersei's death. That could be the reason they omitted it. They may be changing the outcome or didn't find it relevant to include the point if it doesn't play a part in the future, other than just contributing to Cersei's already heightened paranoia. The dead mother, son and father reasons are more than enough for Cersei to loathe Tyrion. No need to add more. In fact, I found it to be a refreshing change from D&D's tendency to overemphasise the sympathetic side of Cersei.