Poison Ivy  

It would be wise to take her to the doctor to confirm it or find out what it is. It may be something else that requires prompt treatment. A pharmacist can tell you what kind of creams to buy. I remember a pink bottle but can't remember the name. Also read somewhere to bathe in baking soda. Thats up to you to try but i have never done it.

Poison ivy is different for everyone. If it's not TERRIBLY bad, don't let her itch. That's how it spreads even more. The doctor can prescribe cortisone shot or Prednisone. Either will dry it up. If you can't take her to the doctor right away, get Caladryl Clear Calamine Lotion. The pink stuff doesn't really work for itching, but the clear does.

The first thing that I'd do is take her to the doctor and confirm that it is indeed poison ivy. Since it is on her face and stuff, the doctor may prescribe a steroid to help her body fight the infection from the inside. One the outside typically they tell you to put calamine lotion (pink bottle) on it to help control the itching.
When my brother had a severe case of poison ivy, we also learned that pool water (with cholorine) helped to dry it out as well.

http://www.health911.com/remedies/rem_pois.htm This has all the information I would have given you, plus some more. I want to emphasize that you will need to wash all her bedding and stuff with a good detergent and hot water to remove the residue, just like this says. I was going to suggest vinegar and the site says that as well. You can put vinegar in your wash water for the clothes and bedding. If it gets worse, get to a doctor. Do not let it get in her eyes.