3 yr old came into contact with poison oak saturay and i didn't know until today when i saw she had patchy hives all over her body. what do i do?

Benadryl (diphenhydramine) : calamine lotion and hydrocortisone creams are some options for managing the itch from insect bites, poison ivy and hives. Sometimes oral steroids are prescribed when extensive.Secondary infections can be avoided by washing with soap and water, trimming and cleaning fingernails, and observing closely for open scratches and redness (in this scenario, over the counter antibiotic creams can be useful)

See a dermatologist: Benadryl (diphenhydramine) is USELESS for this and can have significant side effects. Antibiotic creams are worthless and often make this worse because they are sensitizers making allergic reactions worse. Usual approach is to use a prescription cortisone cream (gel) and sometimes oral steroid. Small dose for 3-year old. Cool water is soothing. It is not contagious, does not spread. You can try OTC hydrocortisone

Unlikely poison oak: Poison oak will trigger blister formation in lines or clusters where it contacted the skin. It rarely if ever triggers hives. Cool compresses can reduce itching and Benadryl can sometime slow the spread of hives. If this continues she should see her doc.