My daughter in law just returned from Pavones, Costa Rica
This evening she has a rash on all of her joints, is extremely fatigued, and continues to have diarrhea.
Could this be a result of her recent trip? A Parasite? A form of Hep C?
It certainly could
What you describe could definitely be a type of hepatitis, probably A, or a parasite/virus, which could be intestinal or more systemic, e.g. dengue fever. You should go to her general practitioner for blood tests and possibly a referral to an expert in infectious diseases.
Hope this helps. Please let me know if you have further questions.