The mansions are very pretty (think Gone with the Wind) and are in a pretty good location. POFQ can be a bit of a trek to the pool and restaurant areas so riverside is probably a better choice if you don't want long walks at the end of the day.
By problems sleeping, do you mean she's a light sleeper? While there are never any guarantees that you won't get next to a noisy group or have them walking past your rooms, you might find there are some resorts that are better than others in minimizing your risk.
IMHO the quietest resort at WDW is OKW , the set up of the hotel with it being in about 30-40 individual buildings of about 10-15 units per building mean that it minimizes the amount of "through traffic" of people walking to their rooms. Again as there are no through corridors, you really only ever hear (if at all) the 4 or 5 rooms that share the staircase with you. This compares very well with some of the more regular designed hotels that have say 100 rooms per floor and 3 corridors per floor (i.e. traffic from 30+ odd rooms could be walking past your door).
Of the resorts you mention I would plump for WL (or to be more precise the Villas at WL if available) They are in their own little wing of WL and as such are considerably quieter than the main building, but it's only maybe 30-40 yards to the main building. WL is likely to be a little more expensive than one of the moderates, but IMHO offers you a better chance of the luxury, ease of travel and peace that you are seeking.
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