Further up and Further in

In our English classes with the children from 5th to 9th grades, I'm reading A Series of Unfortunate Events aloud to them. We choose vocabulary words from the chapters, and the children are supposed to use these words in their own sentences. When I was correcting some sentences a couple of weeks ago, I received this sentence for the word unintelligible: "What ever we'll tell to Mercy she had not having a power to unintelligible."