Hi. I'm Dr. Clark and I'm happy that you have asked me to assist you with your child and hope that you can benefit from my many years of helping parents like you.
Is the rash raised and does it itch?
Then it is likely just a contact dermatitis and perhaps the spaghetti sauce did it or it could be anything that she had on her hands or rubbed against her face. Even new toothpaste, dental floss, lip gloss, etc can do this.
Other than benadryl you should apply a hydrocortisone cream to the area twice daily and the just watch for other areas to break out, as would be the case with poison ivy where the face often breaks out first.
If she starts breaking out all over then you need to have someone take a look at her to see if she needs a prescriptions, such as an oral steroid perhaps.
That depends on the cause as poison ivy can take a week or more. If it was just the sauce and she bathed quickly then perhaps only a couple of days with the topical steroid cream, such as Cortaid.