Barbara wrote a brief manual on the structure of the Farksoo language, and here are two versions of it: an early, very-nearly-complete one and a later, not-quite-so-complete one (pages 4 & 7 are missing). The last page in the gallery is a List of Grammatical Words and Symbols.
Barbara worked on Farksoo, the language of Farksolia, off and on from the ages of eight until about twenty or twenty-one. Here are six pages of notes, followed by the Farksoo-English lexicon, which I believe was the latest version.
If Earthans went to Farksolia they would be sick; first from breathing the air. This is because the air is so thin that when you breathe naturally too much flows through the nostrils and into the lungs, it flows so freely there. The breathing movements of a Farksolian are hardly noticeable, and there is no swelling and rising of the chest and stomach in a Farksolian, at least not so much. Then you would be sick from looking at the sea and the sunset, you are so unused to the colours. Probably you would be sick from looking at the sky and from tasting the curious foods. But you would be used to it in no time.
The Farksolians were great people for inventions. Almost every one of their thirty-six hour days they invented something. One of the most important days was when one invented the marvelous mail system that they had. In the middle of the city was an electric mail station. From it ran underground passages to each house in the city.
Barbara began to formulate her imaginary world of Farksolia when she was a few months shy of nine years old—shortly before she began to write her first novel, “A House Without Windows.” She worked on Farksolia for several years, developing the language of Farksoo with its extensive vocabulary and mysterious alphabet.