I can't speak to the Duc scrambler or Yamaha, but I can talk about the V7 (as I own one).
.. maintenance cost on both is higher than Japanese bikes... what do you think? do you think a Guzzi would be worse than a Ducati to maintain and buy parts for?
The Guzzi will be as expensive to buy parts as the Duc. "What's the total cost of ownership over the life of the motorcycle?" is the real question and that is very low for the Guzzi. The engine, frame and electrics are simple, solid and reliable. The V7 line has kept the same basic 750cc engine design and Tonti frame since it was first made in the 60's. Guzzi has added modern fuel injection, electronic ignition, and upgraded suspension to make the bike a good balance between the old world and the new. It has heaps and heaps of character that I don't think you'll find in the other choices you've mentioned. Styling is great and there are plenty of OEM and aftermarket accessories to change the look of the V7 to whatever you want.
People posted earlier about plastic tanks on the V7. Guzzi went with an all metal tank in 2013 after problems were encountered on the plastic tanks used between 2010 and 2013.
People posted earlier about lack of power for the highway. I disagree. The bike is no superbike for sure, with about 50BHP at the rear wheel, but the tall gearing and torquey engine makes the bike fine on the highway. The V7 is very light weight and flickable. That's a factor to consider if your GF is small in stature. She won't struggle to maneuver the bike under slow speeds.
Suspension components on the stock bike can be better. If your GF is small framed, then the V7 will feel fine for her. I'm 93kg and the suspension on my V7R feels like crap to me. This is a well known problem with the Marzocchi and Bitubo parts Guzzi fitted to the bike. They designed the suspension to perform well for lighter riders so heavier riders tend to bottom out the suspension and it can't be dialed out. There are aftermarket parts readily available that can vastly improve the ride. Check out this video to see what a properly kitted V7 is capable of:
[video=youtube;xd3iwOfSWAg]https://www.youtube.com/watch?v=xd3iwOfSWAg[/video]
The bike is dead simple to work on. If you want to experiment with the fueling, there are free programs available (Gizzidiag and Tunerpro) which will give you full access to the ECU to go to town modifying the engine performance. Guzzi OEM parts are available through dealers as well as online, and cost just a bit more than any Japanese OEM parts. However, out of stock OEM parts can take a very long time to arrive from across the ocean. The dealer network is slim so, if you go on long tours with the bike, you will have trouble finding dealers on your journey. You can't find a better motorcycle dealership than Corsa in Vaughan; they are highly customer oriented and that is
always worth the price of admission for a new bike. The Internet community is also very helpful is solving problems and giving advice.