Hives, facial swelling, high BP due to amoxicillin?

About a month and a half ago my mom was prescribed amoxicillin for a headache she'd been having.  Once she started taking the amoxicillin she developed blisters on her lips and an extremely itchy rash all over.  She stopped taking the amoxicillin.  Since then the rash has not gone away, her blood pressure has gone extremely high, and she has had facial swelling and swelling of her throat so that she had difficulty breathing.  She has gone to the ER a few times and they just keep giving her Benedryl which only helps a bit to relieve the swelling.  This has been going on for weeks and weeks -- any ideas what is going on?  

Thank you

[B_Johnson]

Penicillin allergy would have been acutely severe and not lasted as long.

I do not understand why she was given antibiotics for a headache.

The allergenic agent is most likely something else.

[Mish99z]

Yes I thought the antibiotics for the headache was ridiculous, too -- she'd had a bad headache for about two weeks and her doctor was out of town, a nurse practioner thought it might be a sinus infection (but my mom has never had sinus problems in her life) so prescribed a really high dosage of amoxicillin.  

Thanks for your comment....