Has she sat in a CX-3 yet? I recently checked it out at a dealer in Kobe (along with the new Miata). I really like the CX-3 and I'm seeing them more and more here in my neck of Japan. If you're afraid it's going to be too small, what about the CX-5? Have you seen my video of the Racing Concept CX-3? In the video you can see how it looks and feels from the inside including the back seat and a look at the "boot" (mind you some things are different like the front seats).
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To me, the CX-3 feels like a sportier, taller Mazda2 / Demio with more ground clearance. I love how the front looks as well as the overall styling and here in Japan you can get it with a Diesel (like with most of the SkyActiv range).
Perhaps in your case a CX-5 would be better if you're concerned about space..?