Just a small thing, but it might help a bit - could she ask her Student Services team for a toilet pass/time out card (whatever is in place at her school) so that if she needs to go to the toilet she can leave the lesson with no questions asked. It might help to lessen her anxiety over this a bit.
My DD sounds very similar to yours. She has IBS which is almost definitely brought on by anxiety. It has been sky high recently because she’s had the most awful friendship problems (thankfully on the mend now as she has found new friends).
I don’t wish to alarm you, but just so that you’re prepared, if she’s like my DD, the exams were a major trigger. She was well prepared and looking forward to getting them underway, but on the morning of the first exam she had the most horrendous anxiety related symptoms - throwing up, stomach cramps, feeling dizzy, headaches etc. It took us both completely by surprise, and it continued for every single exam (approximately one million of them, or so it felt).
I’m telling you this so that you can be prepared now. The exams team at my DD’s school were absolutely brilliant. They moved her to a smaller room, helped to calm her before each exam and sat with her when she had to leave and coaxed her back in. I would speak to your Exams Officer and let them know that she’s having these symptoms and that you’re concerned how she’ll be during the exams. Then they can be prepared and look out for her. They have seen it all!
My DD was also offered propranolol by our GP, but this was halfway through the exams and she didn’t want try something new at that point. It works by blunting the adrenaline response, and she felt that she needed the adrenaline to get her through the exams but I’ve heard of others who have found it helpful. It would be a low dose. It might also be worth making an appointment with your GP just so you have something in place if you need it - my DD was prescribed anti nausea medication which she did take, and helped a bit. They might not prescribe anything yet, but you’ll have had the first appointment so it would be easier then to have a follow up if the symptoms do manifest.
I hope I haven’t scared you, and hopefully your DD will be absolutely fine, I just wanted to share my experience as there are things that you can put in place now.
Also, despite her horrendous experience my DD did really well in her exams so don’t panic if she is unwell in the mornings, she will get through it. You sound like a lovely, supportive mum. Good luck!