I think the standard translation is pretty contrived and would argue a wider variety of accepted answers. My own ("she prepares for the start of school") was not accepted. I felt this wasn't perfect, but then again the official translation ("She prepares to start school") doesn't make a lot of sense either
The problem is the reverse translation exercise. Whatever is chosen as the default translation is automatically picked for the reverse exercise. Hence, if contributors wish for a certain Swedish construction to be taught, they have to use unidiomatic English in order to teach the Swedish better far too often than is preferable.
That said, for those sentences contributors do aim to accept more answers than otherwise. Your suggestion is not accepted because it changes the meaning of the phrase, but I'm all for a larger variety of accepted translations which retain the meaning of the Swedish phrase.