Welcome to the forum!
It's really sweet of you looking for answers to your girlfriend's problems
I too have a severe histamine intolerance, and when in a bad period, zucchini is probably one of the only things that doesn't provoke an allergic reaction. I kind of have a love-hate relationship with that vegetable
And most of the doctors just smile when I mention the histamine intolerance, and say 'how can one be allergic or intolerant to something your own body produces?'... right...
I have translated from my language a severe but (to me) very efficient histamine eliminating diet. I couldn't believe how much better I felt once I started it.
Please email me (I can not email you, cause your email address is not enabled) if you would like to receive the diet and I'll send it to you.
This presentation about
mast cell disorders is really interesting and comprehensible /drive.google.com/file/d/0BxK4lGunsmzgVURzTTNncWlFZ28/view
Also, I take antihistamines, but only before bed, to calm my heart down (too much histamine = higher heartrate). But there is an enzyme you can take that breaks down histamine, the DAO-enzyme. There are 2 brands of that supplement I know of (I'm in no way connected to these brands, I just know them because of personal experience): DAOSIN and Histame (can't find the latter anymore, but there is another one that popped up: Nutricology Dao Histamine Digester - I never tried this brand myself). If you take a pill 10-15mins before your meal, you can cheat a bit, like when you need to go out for dinner. It never permitted me to go crazy and pig out on alcohol and lots of cheeses for instance, but it really helps to tolerate normal meals.
There also is this Canadian website for mast cell disorders that has useful information:www.mastocytosis.ca/
I hope this helps...