Excellent question, although I am sorry to hear your daughter has been so upset. In short, here is what I would advise:
(1) Remain on the waiting list for counseling and take advantage of an opening when one comes up. A qualified child therapist is the best professional to deal with, as s/he will be able to fully evaluate the situation and treat appropriately.
(2) In the meantime... I think you can begin two parallel lines of treatment. First, this type of compulsion usually is triggered by some repetitive thoughts of losing control. In other words, she fears losing control so mightily that she is now bearing down and controlling the one thing she has absolute control over - which is her body and its functioning. To lessen the "urge," I would (again, this is a short run solution) offer to compromise some control back to her. Let her know that, even if in the middle of a lesson, she will be afforded the choice of going to the bathroom every (say,) 15 minutes. The time span can vary depending upon her need/wishes, but the point of the exercise is to ensure the control while also encouraging appropriate behavior. If she knows she will have the opportunity to escape the lesson, her urgency to grip the compulsion will (presumably) lessen.
(3) And finally, you can also speak with her pediatrician about the possibility of a low dose prescription of medicine to help loosen the anxiety. A medicine in the class of "SSRIs" can work with teenagers to help ease the biology of anxiety. Again, once the therapist takes over the case, s/he can assess the effectiveness, work directly with the pediatrician, and make sure your daughter receives a balanced, effective course of treatment.
I wish you well. These problems are not simple, as I am certain your daughter is remarkable embarrassed by her actions as well. If you are satisfied with the response, please hit "Accept." That is the only way I can receive credit for my answer. Thanks-
Thanks for this, I did not want to go down the medication route but the situation has now become so serious that it may be useful.
As for coming out of lessons, the school have been really good. They have given her a medical pass to leave any classroom whenever she wants to but in some lessons, to get up and leave draws attention to herself and so she is just refusing to go to the lesson. She has been allowed to sit in a separate room so she can at least still do the work however, the teachers are insisting that she tries to go to the lesson even if she has to leave straight away but this is increasing her anxiety and she often phones me up in tears. Should the school put her under this pressure or are they doing the right thing?
Have them try this: In the short run (and I hope the teacher will work with us here), have her have a "contest" to appoint a student as her helper. Your daughter will win the contest and be appointed as the student helper. That way, it can be set up that every 20 minutes (or so - again, this depends upon your daughter's tolerance) she can be dispatched on some "errand" to run something to the office, deliver a paper to the lesson in the next room, seek out a teacher with a message, etc. This errand may be a ruse or it may be legitimate, but it affords a shred of dignity to a girl who is obviously embarrassed. Changing her "role" may give her the cover she needs.
This will work best if she is not forced to attend every lesson, but it is a beginning to achieve some balance while we await proper treatment.
Hope this helped. If you are satisfied with the response, please hit "Accept." That is the only way I can receive credit for my answer. Thanks-