Supposedly allergic to estradiol
Trans girlfriend supposedly allergic to estradiol.
Ah, ha ha ha ha, NO.
Most likely, she has an undiagnosed parasitic infection and getting the correct hormones to properly support her immune function as a person with a sex hormone syndrome is causing itching because it's causing her body to more effectively combat the infection.
I would test for trypanosoma.
Or just order Zithromax or levaquin from Mexico without a prescription if she ALSO gets fingernail issues on estradiol.
If it's not trypanosoma, look for other parasitic infections.