Well, if it done on a keyboard at all: My teacher from a decade ago(Hammarstrom), started the class with pentatonics(but just the black keys). You can't really go so wrong when you use only the black keys, and there are major as well as minor chords you can use. That would be a good introduction to the idea of major and minor. As soon as there is general understanding of simple rhythmic device, using BH, and more than one note at the same time, then maybe you can move on to white keys only, familiarize your student with the idea of a scale, and start the memorization of Every Good Boy Does Fine, etc.
Funny thing is, i took the class when i was about 15, so i had been composing for 3 years already, but it still beat having any other elective. Some other good early stuff to get into is counting out simple time signatures, and fundamental forms like the 12 bar blues. Just whatever you do, don't get into Simon Glass, it's just bad juju. You couldn't even count the naive teens who actually call that art. Lmao, how could they call a minimalist an innovator?
There's an aweful lot you can do, but just keep the interest going, keep the need to examine structure and you can have the young lady actually wholeheartedly wanting to be a classical artist in a few years. Sounds like a hell of a lot of fun, i always wanted to teach that class myself.