If your sister is on multiple meds, you should check for drug/drug interactions as well as drug/food interactions. Do a search for 'drug interaction guide' - there are several databases available. IMO, the best drug databases use multum data.
In the meanwhile, check all her meds [OTC and prescription] and vitamins on the MedLinePlus drug database:
Also research any supplements she may be taking, just in case.
BTW - also do a search for 'grapefruit effect'. There's a compound in grapefruit that is preferentially metabolized by one of the key liver metabolic pathways used to metabolize many meds. If your sister is taking any meds that are metabolized or broken down through this pathway, and if she also consumes grapefruit [juice or fruit], this may compound her problems.