It appears your daughter has an allergic reaction to the Omnicef.
I agree with the advice given by silverfox67 that you should take your daughter to the doctor. A note will have to be put on her medical records that she has had a reaction to the medication so that it is not prescribed to her again.
As well as an antihistamine that the doctor can prescribe for your daughter, you can also apply calamine lotion or Caladril to help stop the itching. Natural live yogurt will also help to cool down the itching.
Make sure your doctor drinks plenty of fluids so as not to get dehydrated. Ensure that she is wrapped up warm and wears a hat to cover her ears or wear ear muffs when she goes out.
Stop the Omnicef immediately and give her an antihistimine. She must never have that medication again as she is allergic to it.
Sometimes when we continue to take a med that we are allergic to we get a more serious or severe reaction to it...
Stop the meds and take her to the doctor!