First, if you are dealing with an aggressive woman skier, remember that most women's boots will have some sort of compensation to reduce heel pocket volume. Especially the Krypton Lotus, which is a narrow boot to begin with.
My interpretation of her experience with the Krypton Lotus is that A) the stock insert just wasn't doing it's job, as stock inserts rarely do. The slipping in the heel was a result of her narrow heel and lack of a proper "heel cup". This "cup" is exactly that, it will grab all around the heel and prevent it from sliding side to side and if the boot was fitted properly, up and down. B) Were the boots sized properly? Many demo centers may just ask what size street shoe is worn and dole out the corresponding boot size- even though there is always a discrepancy in street shoe-to-ski boot sizing.
The Krypton Lotus was a great boot last year, especially for more aggressive women with narrow feet. I suspect a poor size fit and insufficient foot support stemming from an inadequate insert, thus her sense of loss of control.
I suggest a consult with a pro fitter and an evaluation for a custom or off the shelf replacement insert.
Benjamin Goldstein, C.Ped
Wachusett Mountain - Mountanside Ski and Sports Shop