Sounds like anergy, which means no reaction to skin tests despite the use of things that should provoke a reaction (such as histamine).
Autoimmune disorders can cause anergy, but I agree that an Immunologist should be consulted about this situation.
Did she show any allergies on the blood allergy tests?
Chronic Lyme, Bart., Gluten & Sulfite Sensitivity, Many Food/Inhalant/Medication/Chemical Allergies & Intolerances, Asthma, Gut dysmotility & non-specific inflammation, Lupus, Osteoporosis, etc.; G-Tube
Meds: Flagyl, Domperidone, Claritin, Singulair, Andrographis & other herbs, homeopathy, supplements, etc.