impossible to give you an answer without hands on/eyes on your wifes feet.
if your info is accurate about the widest past of her foot being 91mm, than she will be fine in the LV. the LV in her size will be about 93.5mm wide. the 100 version in her size will be about 96.5mm at the widest point.
common sense would bare out that if there was too much space in the boot(like the 100mm version), your wife will attempt to contain her foot by over buckling the boot on top of her foot. this will result in cold toes due to either lack of blood flow or nerve compression.
so, your boot fitter was doing real well in selecting a LV model boot, however he seems to be tripping over himself the more he talks. no matter the level of skier or the aggressiveness of your wifes skiing style, there would not be a benefit of putting her in a boot that has more room vs less room.
Edited by starthaus - 10/16/14 at 9:25am