Bubbleator Levels and repetition of items

In Bubbleator (and in Mumzi Madness) my daughter feels like the games never changes, or changes glacially slowly- she says its always either fruits, shapes or numbers, and that even within these categories the items don't change or increase in number rapidly enough. Can you explain how these games are supposed to work and when she can expect the get new items to learn? She is getting bored with the repetition of things she feels she knows.