I am LDS. My parents-in-law drink tea, coffee and other things that we choose not to drink. Right now my kids are small, but this year I'm sure dd is going to ask specific questions when we see them this week.
In the past we've just explained that X is grandma's drink and not for sharing.
Right now we have started explaining about different people making different choices. If you are traveling together, then take your tea/coffee, etc. yourself. Don't expect an LDS person to serve that, just ask if you can boil water. Also, talk with your friend to find out what she's comfortable with.