I study public health and I love to read, so I know there are an endless selection of interesting books to choose from. "The Hot Zone" and "The Immortal Life of Henrietta Lacks" come to mind, but they're both popular so she might have already read them. If she has a specific interest or favorite pestilence (I'm personally fond of Spanish influenza!) then it isn't hard to find a book on Amazon.

Alex and Ani bracelets are apparently popular with yoga goers, and there are a ton of charms to choose from.