Background: After several years of estrangement, DH and I have resumed visiting with his sister. SIL was a drug addict for several years, finally cleaning up her act about 5 years ago, after contracting Hepatitis C. Most of the visiting falls to me, which consists of us going to lunch and shopping trips.
She lives about 45 minutes away by car, so when I drive to visit her I usually have a bottle of soda or water to keep me hydrated. The problem I have is when she gets into my car, within 5 minutes, she is drinking from my bottle. I've tried to solve the problem by providing an extra bottle for her, but she will drink from her bottle, then from mine. If I order other than water at a restaurant, she will drink from my glass as well. Of course, I don't want to drink after her, even though I know there's only a minimal chance that I can catch Hep C through saliva.
My question is: How do I handle this without insulting her?