Paragraphs a and b are linked -- leaving the scene of any injury crash is a Class 4, and subsequently failing to notify the authorities within 30 minutes elevates to a Class 2, if a person was injured, and Class 1 if a person was killed, which is the case here. Since she failed to meet her legal obligations in both paragraphs, she committed a Class 1 felony.
The driver left the scene of the accident. In all likelihood, she cannot be charged with failure to report the accident because she was apprehended shortly after leaving the scene. Luckily, the district attorney knows more about the case than you do and is capable of correctly interpreting the law.