Thats a really nice looking Motobecane Mixte. The frame has a Vitus 172 tubing sticker on it so its made with double butted cromoly tubing. I'm not familiar with Vitus but here is a short history of Vitus you can check out. *Vitus history by Norris Lockley

I would say a french bike made of french tubing will most likely have french threading on the bottom bracket and head set.

If the rear spacing is 120mm it would be easy to respace the rear to 126mm to fit a 7 speed cassette. Sheldon Brown's website is a treasure trove of information on upgrading old bikes and what will work and what won't. Upgrading Older Road Bicycles That bike does have 15 speeds already with what looks like a fairly wide gear range so you may be able to leave it the way it is. Although I would be tempted to at least replace those derailleurs.

Overall that would be a very nice bike for your girlfriend to tour Europe on. Maybe look at what you can do to upgrade the brakes if she's going to be carrying a load.