Thanks to everyone for the very helpful suggestions, especially to those who said 'tell your friend' - I will, it will be less embarrassing than her finding out when we have arrived!. Thanks also to anxious gran for the suggestion that I give my friend permission to poke me in the back. I will definitely bring a selection of ear plugs for the poor woman to try, and I will also get some nasal strips, and talk to my GP about fluticasone.
I don't smoke and I'm quite slim, so that's not the problem. And because I live on my own now, it's not something I worry about much, so I'm really grateful for all the ideas.
Lastly, thanks to Shortlegs for the brilliant suggestion of just staying awake for the week, though since it's a walking holiday, that will be a challenge.
I also hadn't thought that my friend might be a snorer too, and worrying about the same thing!