I have a 40D, 50D, 7D, 1D3 and a 5D2 so I'm well acquainted with all the cameras you have mentioned. Given what you have said about her preferred subject matter the 5D2 would complement the 40D best. If she doesn't shoot sports and action, or pick off wildlife in the distance I don't think buying another cropper would be as beneficial as going full frame.
However, I'm puzzled by the 100-400 comment. Why does she want one of those for shooting people and lanscapes. That would be a general purpose lens typically for sports and wildlife. I have that lens too, but it usually goes on one of my crop bodies, because I use it when I want more reach. Of course, if she wants to shoot these things too then the 1-4 on the 40D and the 17-40 or 24-105 on the 5D2 would be a sweet combo. I really can't see her benefitting from a 1D anything, unless I've missed something.
BTW, the 7D is a wicked camera, with an incredible feature set and performance, but it's still an APS-C sensor and will not work magic on IQ the way full frame will. That's not just in relation to noise/DR etc. but the control over shallow DOF that can be obtained when shooting people and the detail that can be obtained for landscapes. As for the 50D, I bought mine as an upgrade to my 30D. While it is a better camera than the 40D, it is not going to make the kind of difference that a 5D2 would make, or even a 7D. Also, 17mm on the 5D2 will be seriously wide. Nice!
Having said all that, what exactly does she not like about the 40D? It's hard to come up with a solution if you don't know the problem. Given what you said she shoots, I'm not sure why she would be unhappy with the 40D. What sort of ISOs does she shoot at? Is the problem noise, AF, some feature she wants that the 40D does not have, what?