That's a lot of gear. Are you actually going to be carrying stuff when you are trekking (maybe there is a group minibus) or even walking around town ? Going on a photographic trip for work is different to going on holiday with g/f, in my opinion (maybe I had the wrong g/f's . . .).
If you take a lot of gear, apart from the practicalities of lugging it around without spending your whole time worrying about it getting nicked, you will use most of it almost not at all. It just isn't worth the hassle.
All my trips have involved one "good" film camera and an absolute maximum of three lenses. I'd say take one M body, a 35/50, (according to personal choice) and a 21 or 15. That's it - plus extra film of course. Your girlfriend can carry a film-compact or digital p+s (or her own M), so that will be adequate as backup. For peace-of-mind, it could be possible to get the body serviced before the trip, and also leave enough time to test it thoroughly.
Enjoy the trip . . . after all, if it was just for photography you would be using 10"x8" sheet film, wouldn't you ?