Hello and welcome to HCM
From your history and description it does seem like an
allergic reaction. You will have to narrow down the possible cause by checking for any history of new food intake, insects bites, stings, plants or weeds playing outdoors(affecting the limbs), pets, etc.
Since you have mentioned that she was taking
amoxicillin, definitely keep in mind chances of a
drug allergy, commonly seen with this drug. The steroids and
benadryl should control her allergy.
But drug reactions do have a tendency to get severe. Watch carefully for spreading area of discolouration, redness, sores, blisters,peeling skin or bleeding, esp on the lips, mouth, near eyes, genitals etc. In case of such symptoms report to a dermatologist immediately.
If not, apply a soothing lotion on the rashes for now.
DO
consult a dermatologist in a couple of days for a review and to check the progress of the symptoms.
Hope this helps.