It makes more sense to find a cartridge to match the preamp.Ron -- Note that she already has a 5mv cartridge. No moving magnet or moving iron cartridge, to my knowledge, is going to provide a great deal more output than that. I believe there are some cartridges that approach 7mv, but that is less than 3db greater.
So if the root cause of the problem, as I suspect, is the level of noise generated by the phono stage, changing cartridges will not improve signal-to-noise ratio, and therefore will not help significantly.
Regards,
-- Al