(B) Reference Book on Drug Interactions
(C) Literature that came with the Medications
Yes, you can actually call a pharmacist and ask for detailed drug-interaction information, even involving nutritional supplements and herbs.
But there are sites on line that do that for you, too. When people discover dangerous interactions, they tend to publicize them.
Nonetheless, I do suggest your friend do the follow-up, as there are different categories of blood pressure lowering-medications, and you could waste a great deal of time not knowing which she takes.