My daughter is on amoxicillin and i gave her motrin to help with the pain. she has poison ivy, can i give her benadryl (diphenhydramine) too?

Yes: Poor girl! You didn't say what the amoxicillin is for, and the pain is from..? Anyway, it's fine to give benadryl (diphenhydramine) along with ibuprofen and amoxicillin. No interactions. Just make sure she takes them with food so she doesn't get nauseated. Aveeno bath, calamine lotion help the poison ivy as well. If it continues to spread, or is on the face or genitals, call your pediatrician for stronger meds

Topical hydrocortiso: The best Benadryl (diphenhydramine) can do for her is to make her a little drowsy thereby making the itching more tolerable. Topical cortisone works far better and you will need to wash every item which had had potential contact with the ivy with laundry detergent else the resin will cause new lesions again and again.