YMMV but it might be something useful to try with your wife.
In this case the sound that arrives at the eardrum does not conduct through the middle ear bones to the cochlea.
Wax will only cause a slight drop in hearing thresholds.
This can be determined with a standard hearing exam.
Recently tried a demonstration at SF's Exploratorium which involved biting a metal bar, and the result was incredible!
Most bone conduction headphones I find when searching (eg AfterShokz) appear to rest against the bones around the ear, so I'm not sure if they're as effective.