There's not much about Mary's health at http://www.peterpaulandmary.com/ - Here's the entire text:

Mary Travers of Peter, Paul & Mary Undergoing Chemotherapy Treatment Though Mary Travers is currently undergoing chemotherapy for a form of Leukemia, a full remission of the disease is expected within a few months.  Mary looks forward to touring again with the trio soon, and is grateful for the well wishes that have come to her from all over the world. Email may be sent to:   ForMary@peterpaulandmary.com Mailing address for cards or gifts  (no flowers or plants, please): MARY TRAVERS P.O. BOX 4720 GREENWICH, CT 06831

Maybe nothing more needs to be said.
-Joe Offer-