What was she fed before she died?
Broccoli and cabbage are not good in large amounts for guinea pigs or any herbivore as they produce a lot of gas and can cause bloat. Fruits should be a very small part of the diet. The best greens for cavies are a variety of leafy greens such as mustard greens, kale, parsley, endive, escarole, dandelion greens, Romaine lettuce, etc.
Also, you didn't mention hay. Like chins, cavies should have an unlimited amount of hay at all times. Hay should be their staple. It is very important for their digestive health.
Also, was any vitamin C given to the guinea pig? Guinea pigs cannot produce their own vitamin C and get it solely from their diet. Even though pellet formulations contain vitamin C, it is a water-soluble vitamin and degrades very quickly which is why they should be supplemented with vitamin C rich fresh foods and if needed, a vitamin C supplement.