damn it not again

So my son Xavier is anaphlyactic to peanuts and egg, and until recently we didnt know who had the "allergy gene" as my ex and i both dont have a history of allergies in our family.
In the last week though Aliana has had a rash covering her ears, cheeks, torso and bum just like Xavier used to get before we got diagnosed.
I tried thinking of what it could be and came up with the fact i had quiche for dinner at a friends house and she had a feed of milk afterwards (breastfeeding).
Its definitely not heat rash because it doesnt calm down and its not hot today yet its still pretty bad. And teething rashes dont spread to the body like that and there is no other sign of teething.
She has a different father than my son and my fiance is refusing to believe that his little girl could have an allergy. he even went as far as saying she wasnt "weak" as Xavier (my son with allergies who was in hospital with all sorts of illnesses as a baby) that got me really upset, but thats not the point.
I dont really know where to go from here though. Golden Bay dont even test for allergies and seeing as though Xavier is anaphlyactic wouldnt it need to be done in a hospital environment?
I dont know if i am overreacting or not, i spose i am concerned and just need to vent. I dont know how i would handle having 2 anaphylactic children. its hard enough with 1.