It's important to keep a student with a chronic health condition safe and happy in class. One step you can take is to understand that there isn't a one-size-fits-all plan for dealing with chronic illness.
Part of the reason it's important for you and your staff to read up on the illness and to communicate with the student's guardian is that there isn't one umbrella formula for accommodating a sick child at your studio, and the same dancer won't have the same needs every day.
A dancer with type 1 diabetes might simply need to grab a snack when her blood sugar levels drop, but she could also act confused if her levels are too high. Whether it's easy access to a bathroom, an inhaler on hand or something else entirely, having flexibility will help you learn the nuances of your student's needs over time.