Your wife has developed a moderate to severe allergic reaction
given the symptoms of nausea, vomiting, generalised urticarial rash, near fainting episode. The last symptom is due to sudden histamine
release and loss of blood pressure control that is defined as anaphylaxis
So she had anaphylaxis and going to sleep is NOT a good sign.
Please call the Ambulance if she remains unresponsive and you are unable to feel her taking breaths or unable to get a pulse.
She may be truly asleep as some people get drowsy on antihistamines, but sedative antihistamines should only be given is such a setting in a hospital.
She definitely needs blood tests against the entire nut panel, but should be done after 4 weeks.
Even if the tests are inconclusive or borderline positive, she must AVOID ALL NUTS for life.
An emergency kit with Epipen, cetirizine
and asthalin inhaler (if asthmatic) MUST be available to her or at the house at all times.