Answer:
The insurance company is not liable because no accident happened. The flowers spoiled due to a failure in the transportation process, not due to an accident. The principle of insurance involved here is the principle of proximate cause (or nearest cause).
This principle states that the insurance company will only be liable for losses resulting from an event covered by the policy. The insured event that caused the loss must be the nearest cause of the loss. In this case it doesn't apply because the insured event was an accident and the proximate cause was an error in the transportation process.