I am in Canada if that makes a difference, we can't get some of the same things in our local co-ops and tractor supply!
Any help would be greatly appreciated!
There are several respiratory illnesses/diseases that can cause sneezing and mucous.
Is there any way you can have her tested?
Most antibiotics will treat the symptoms, but will not necessarily "cure" the disease depending on what it is. Also be aware "most" respiratory illnesses are contagious and make those exposed (even though some never show symptoms) will be carriers for life.
Wondering if the breeder is already aware of a problem since they are willing to accept the return of "sick birds"?
Did they give any indication of what the birds may have?