It seems to be focused more on conversational languages, as opposed to written ones.
DD is interested in Greek literature after reading some excerpts from the Odyssey, and wants to learn to READ Greek. I realize that the Mango programs are probably not the best choice there, but they do have the attractive property of being, well... free.
With Greek, it's not just the conversational vs. written aspect you have to consider, it's the differences between modern, Classical and Homeric Greek. Modern is different enough from the other two that, if it's all Mango provides, it wouldn't be much help for your daughter, given the interests you describe.
