She can't be charged with driving under the influence of drugs, because insulin is not a proscribed substance - it's not a drug, for a start. But without testing before driving, the insurance as has been said, will be invalid. She would also be charged with driving otherwise than in accordance with a license (that's the condition of testing), and if she has a hypo and an accident, dangerous driving. Causing death by dangerous driving will get you 10 years inside. The DVLA will take away her licence, probably for good, whatever disqualification the court imposes (usually 3-5 years for dangerous driving, 3 is the statutory minimum, no appeal) and there is a compulsory retest - she would only be returned a provisional licence.
The charges would likely be different in Scotland, where only impairment is tested, not necessarily with alcohol or specific drugs, but the result would be the same.