Identifying the area of law that is most relevant is important, because then you know where to go to find the concepts and rules needed to resolve the case.
The facts in the case study refer to various areas of law. But what you are looking for is the area of law that is relevant to the dispute that has arisen between FoodCo and GlassCo. With this in mind it is easy to discard most of the areas of law listed in the question.
Although Astrid and Ben both act as representatives of their companies, the issues raised by Astrid do not involve corporations law.
Although the sale of goods will involve the transfer of property rights to the buyer, there is no issue between FoodCo and GlassCo in this regard.
The facts do not suggest that FoodCo is relying on a right arising in tort law to claim compensation from GlassCo.
There may be elements of consumer protection law to be considered, but these would not be the most obvious cause of action at the outset.
Although Astrid and Ben are both acting as agents of their companies, no questions of agency law are in dispute.
From what she has said, it is clear that Astrid is complaining that FoodCo has not received exactly what GlassCo had bound itself by contract to deliver. This suggests that she is relying on a breach of contract by GlassCo. The rights she wants to enforce are contractual rights. Contract law is the area of law that provides FoodCo with its most likely cause of action.