Well, it may be tangential, but I'll answer because it is a topic dear to my heart...

Our DD sounds very similar, except we do have a piano and I play, so that has made it easier for her to learn on her own terms. This summer, after a lot of discussion, she did take piano lessons, with the stipulation that it be for the summer only (she also values her free time and has a full plate during the school year). I was lucky to find a teacher who understood what DD wanted from her and was willing to take her on on those terms. They also worked out of a theory textbook each week. DD practiced very little; she is an excellent sight reader, but I suspect this experienced teacher could see through that. But in this setting, that was fine. (The teacher did mention at the end of the summer that DD would be an excellent pianist if she decided she wanted to work at it, but that's a different thread altogether). If you can't find a teacher who will be flexible (or if your DD still balks), does your school offer anything along those lines? The middle school theory course here is half workbook theory, half composing, and the school subscribes to several software programs that facilitate this (DD didnt want to take the course- I suspect she thought it would be too easy, and she may have been right, but she has used the software thanks to her band teacher).

I can't bring up the names of all the programs off the top of my head, but there was a thread about composing that was pretty good some time ago. Noteflight is one, I think there is one called Sibelius, but if I recall correctly it is a paid subscription. GarageBand has some cool features- DD went through a stage of recording herself playing multiple parts and then putting it all together- pretty funny but neat. Also, I don't play guitar, but i wonder if learning the chords and progressions would serve the same purpose? Or even ukelele or something like that?