claw is right - you need a plan in place to help with the toilet issue (I know this is possibly the tip of the iceberg, but it is an important tip!)
dd1 refuses to use the toilet at school (right form botched attempt at potty training by incompetent nursery - she is now 6!)
we work closely with the school, as the knock on is huge. dd1 regulates her drinking so that she doesn't need to go at school, which has obvious health implications (some days she will only drink 100ml or so, all day)
Katy, you need to be jumping up and down and shouting lots about this.
you disagree with the school's and professionals' views on how your dd should be treated (and with good reason, imo), and now she is beginning to school refuse - you need to be flagging this up and linking it to the school, the LEA, camhs, everybody really.
was she refusing school as often when she had (limited) support last term?