tip: buffy gen teen AND "no archive warnings apply"
This is a really splendid story and you must have props for writing it. Polyhymnia is such a marvellous character and you've captured her here so well, from her change of minor to her moody snow-watching to her slow pre=occupation with the trouble of time-splitting.
The mystic thematic is natural as opposed to forced and well thought out. You haven't just made Poly a bungler through time. Nothing happens for an accident. She is waking up to an awareness that Charles Wallace is quite thrown into. Her uncertainty in conflict with her push to trust her instincts is really wonderfully Poly. In the end, it's not that she really is unsure, it's that she does not yet understand how to communicate her sureness to others who would worry other than a hand squeeze and a "Trust me." Perhaps in the end, that's all it takes.
Her relationship with Canon Talis is portrayed in a really fabulous way. There are complex and subtle overtones here concerning her Uncle Father. He is mentor and she is student, with all the baggage that goes along with that. I read shades of Merriman and Will in this, but I am predisposed to do that.
I would love to see more of this from you. Thank you for writing it everso.