After years of vibe usage [external], SO cannot orgasm unless Hitachi is on her clit, now set on max-speed.
She does still enjoy penetration [while vibing herself]
I am concerned that she is becoming de-sensitized, which will continue to progress.
Any advice please?

Dear PleaseAdvise,

It truly depends on the age of your SO. As women advance further toward perimenopause, their vulvas can become less sensitive and need more stimulation, particularly in order to achieve orgasm.

At this point, I would worry less about her becoming "desensitized" and cherish the fact that she is orgasmic with or without penetration, as long as her clit is being "vibed." Later on, as her tissues become less plump and thin out due to lack of E3 (estriol), she will go back to being more sensitive, perhaps almost tender in the clitoral area, again.

Women in their 40s often require "hard fucking" or "hard stim" to get off. To some men, it's a total turn-on; to others, it's cause for concern.

Don't worry, just go along for the ride as long as it lasts
The Love Goddess

Once again, you are right on the money, LG.
She is 51.
She does often demand the hard deep fuck in order to cum [and she comes intensely] , while being vibed concomitantly.

abstinence for a while, it should undo the desensitization
but desensitization should come back quickly so you'll have to wait again for an intense orgasm