Well, you came to the right place.... welcome!
Poor baby! My girl gets hives (very bad) from something outside.. still not sure what exactly because her list of allergens is so long we could not narrow it to what got to her. Anyway,you can give her more than a 1/2 benedryl... my two bullies weight 60lbs and they get 50 mg in the AM and 50mg in the PM. Getting the full blood screen allergy test is a great decision it will give you all the answers you need.
In the meantime, try to get grain out of her diet... grain and chicken seem to be big issues with bulllies. Also, I am going to tag @Libra926 she has a famous stew for Vegas that is all veggies and you could possibly feed that till you get the allergy results back.
Good luck and keep us posted.