I'm LDS too (gee...we're coming out of the woodwork!) :)
I do not expect my non-LDS friends to try and behave as if they were LDS in my precense. That said, we do have a rule that will always stand that we do not allow alcohol in the house (or cigarettes, etc). But coffee is not equal to alchol. Hmm...this is a tough choice. (and I actually LOVE the smell of coffee...) My son already knows that we do not drink coffee or smoke (we have neighbors whom we see all the time who do) but that some people do not believe the same things that we do and choose to take such things into their bodies. I would not have a problem with a friend coming over with a to-go cup of coffee in hand. I don't know how I would feel about a friend preparing her coffee in my kitchen, though.
Like has already been suggested, I'm sure she would be open to you asking her about her preferences!
Have a great trip!
Oh, and in the word of wisdom it says we should not take strong drinks into our body, meaning green or black tea and coffee because it is not good for our bodies. There is no hard fast rule about caffinated soda. It's personal interpretation and revelation at that point.