A year ago he nearly died after eating a toaster waffle with no peanuts in the ingredients, but that we later discovered was manufactured in a facility that processes peanuts. Fortunately my ex-wife overcame her fear and jabbed him in the leg with his epipen - that's what saved his life. He had difficulty breathing in the ambulance, but that cleared up by the time he got to the ER. A follow-up with Benadryl and steroids was required to take care of any lingering effects.
Do you know what caused the reaction? I assume your daughter will be referred to an allergist and will get her own epipen. If she doesn't, definitely ask "Why not?" I know you are looking for reassurance, but you should know that the next reaction could be worse. However, if you're careful there may never be another reaction.
We had to file a 504 (disability) plan with my son's school to make sure they took peanut butter off the school lunch menu and provided him with a peanut-safe table apart from anyone who might bring peanut butter from home. I always discuss his allergy with the kitchen staff when we eat out, and of course check ingredients when shopping.
Here's a good link:
http://www.foodallergy.org/Best of luck to you!