Answer:
A parasitic bacteria contaminated her food.
Step-by-step explanation:
Parasitic bacteria like Clostridium botulinum or salmonella cause food poisoning. The symptoms of food poisoning appear within a few hours of food ingestion or may be after 6 to 10 days. All the symptoms listed here like nausea, fever, and diarrhea occur due to food poisoning. It is clear that she is suffering from food poisoning and since these bacteria caused problems to Arianne without benefiting her in anyway, they are considered as parasites.
Also, mutualistic bacteria are the ones which live in the body of host and provide certain benefits to the host, a commensalistic organism is the one which gets benefits from the host without harming the host, a predatorial organism on the other hand kills the another organism in order to get benefits but in the question nothing like that is happening to Arianne so all these options are incorrect.