Diabetes is a disability, so reasonable adjustments is required including mobile devices for monitoring. We had a case in a school where supply teacher did not allow and school were taken to court. You will need to log how often (time length) does pupil need to eat / check glucose levels and then this should be applied in the exam. Can the checking be tied in with rest breaks? Let pupil keep the phone on them, (just in case there is an emergency dip brought on by stress) but ask pupil to intentionally take out and check during breaks, unless emergency trigger.
Whats the signalling system for pupil to tell you there is a problem in the exam?