I agree with the folks who tell you to let her pick her own -- machines today have so many features, only she can tel you which ones she would find most useful. Be aware, many of the Brothers are similar to the Janomes, but they cost less.
When I need real heavy duty stitching, I haul out my Elna Supra (vintage 1976). When I bought it, they told me that it would go through anything if I used the correct needle -- and I even sewed through cardboard. (Is she using a new Jeans 18 needle to try to get through the thickness?)
I had the Janome 6500 and now have the 7700 -- love them both. I got the 7700 for the freearm and the better lighting, as well as accufeed. The 7700 sews through most thicknesses with a little encouragement, and is a dream for piecing and regular piecing.