I am the fourth child in the family, and the problem occurred because our mother was diagnosed with colon cancer. It seems that it was a consequence of her previous condition ulcerative colitis (she had it for years). She is under radiotherapy now and has serious problems, nausea and constant vomiting. Doctor prescribed her with Granisetron and I wonder how does Granisetron interact with hormonal contraception?
As far as I know there is no interaction between those two, but the best advice I could give you is to inform her doctor of the medications she has been using before this situation, in order to avoid possible complications. Granisetron will surely help her with her troubles she got from radiotherapy. The efficacy is almost 90, so you should not worry about those symptoms anymore.