Well, the problem with treatments intended for IgG allergies is that...
oh, let's see.... how to put this...
they aren't treating ""allergies"" (because that isn't what "IgG" anything actually IS) and therefore, they won't work on... um... actual-- you know, "real"-- allergies involving IgE.
Now, immunotherapy regimens CAN work for IgE allergies. This is the basis of "allergy shots" and also the basis for some desensitization protocols for food allergy currently conducted at a few major research centers. I cannot iterate strongly enough, however, that this kind of thing is-- well, it's not amateur night. NOT a "hobbyist" project. NOT for physicians who "dabble" in food allergy. Most DEFINITELY not a "DIY" project of some sort. In current clinical practice, outside a TINY handful of people doing this in clinical settings for regular patients (and even that is highly controversial to say the least), this is not for people with anaphylaxis history to begin with.
The description that you've been given-- who the heck knows what kind of treatment this actually entails, and whether or not there is actual allergen exposure happening. In any event, the partially plausible part of things is the "low dose" exposure. This could mean SLIT (there are trials ongoing, and a clinic in WI which has been doing it for years-- though results are somewhat mixed, honestly), it could be OIT (again, clinical trials in a few locations, and a handful of allergists going ahead of those trials to offer it to patients), and it could be some whacko holding-vials-of-the-allergen-and-muscle-testing thing.
Injections? HUGE red flag for me. The last injection immunotherapy trial that existed, someone in the study group DIED.
So-- NO, NO, NO.
This stinks to high heaven of CAM medical practice going off-trail and stomping about where angels rightfully fear to tread. Anyone that WOULD claim to treat IgG allergies and IgE food allergies....
RUN. Run for the hills.
These are the kind of practitioners that can kill people with their ignorance.
My apologies if this is overly blunt. I'd walk away from any medical practitioner that claims to treat IgG allergies, and I'd double-time it if they added IgE to the claim.