It is when the levels are high AND she has ketones present in her urine that is dangerous, DKA, Diabetic Ketoacidosis.
Some of the symptoms of DKA can be any or all of the following, tiredness, excessive urination, thirst, stomach pains, nausea and vomiting, fruity breath odour, dry skin and mouth, flushed face, deep rapid breathing etc. That is a medical emergency and would mean A & E by the quickest means possible.
Conversely, when the blood sugar levels are way too low that too can quickly turn into an emergency if the proper remedy for a hypo is not given in time.
You should have been told the sort of levels that your daughter should try to maintain to avoid both circumstances.
Ken / Sue