If this is a senior and wants to do a class 1 solo does it have to be xylophone? As said below the 4-mallet solos are probably "easier" than the 2-xylo ones; e.g.Yellow After the Rain, or the Ford book. These are achievable with some work.
What about doing another class 1 percussion solo since there are several categories to choose? There are snare, timpani, muti-percussion, or drum set that could be other options for your student.