Irritable Bowel Syndrome with Diarrhea (IBS-D): Given the patient's history of possible IBS-D, the symptoms of diarrhea after eating salmon could be an exacerbation of her underlying condition, triggered by the consumption of a specific food item.

Food Poisoning (Salmonella or other pathogens): Salmon can be contaminated with bacteria like Salmonella, which could cause gastrointestinal symptoms such as diarrhea.
Scombroid Fish Poisoning: This condition occurs from eating spoiled or contaminated fish, including salmon, and can lead to symptoms like diarrhea, abdominal cramps, and vomiting.
Lactose Intolerance or Other Food Intolerances: If the salmon was consumed with dairy products or other trigger foods, the patient's symptoms could be due to an intolerance rather than an infection or IBS-D exacerbation.

Inflammatory Bowel Disease (IBD): Conditions like Crohn's disease or ulcerative colitis can present with chronic diarrhea and must be considered, especially if the patient has other symptoms like weight loss, blood in stool, or persistent abdominal pain.
Celiac Disease: An autoimmune reaction to gluten could cause similar gastrointestinal symptoms, and it's crucial to rule out this condition due to its potential for long-term complications if left untreated.
Giardiasis: An infection caused by the Giardia parasite, which can be contracted through contaminated food or water, and can lead to chronic diarrhea.

Parasitic Infections (e.g., Anisakis): While less common, parasitic infections from undercooked or raw fish can cause gastrointestinal symptoms.
Allergic Reaction to Fish: A severe allergic reaction to salmon could present with gastrointestinal symptoms among other systemic reactions.
Tropical Sprue: A rare condition that affects the small intestine's ability to absorb nutrients, potentially causing chronic diarrhea, though it's more commonly associated with travel to tropical areas.