If you're insisting on a C1, though, look into All'Antica by Goeyens. Andante et Allegro by Ropartz isn't impossible. Concert Etude by Goedecke is good too, if she can tongue, has fluency, and has that A consistently and well. The Kennan Sonata is also rhythmically difficult and requires maturity, but it isn't as technically (runs, range, etc) difficult as some other pieces - but it's LONG and not quite as tonal as she might want.
The "easier" or "introduction" Class 1 solos are now all Class 2 solos, just like with other instruments. Unless she is 100% ready to commit and work her tail off, give her a tough Class 2 and let her work her way up next year. There's no sense giving her a 1, and having her get a 3 on it, when she could've gotten a 1 on a Class 2.