It's rare that a child outgrows a nut allergy, but it has happened. Your best bet is to keep her away from nuts altogether until she's at least five, then have her re-tested--that includes foods processed with nut products. As for severity, no matter what anyone tells you there is no such thing as a mild peanut allergy. From now on or until she no longer test positive for the allergy, the epi-pen should always be with her. My son only had minor reactions--rash, runny nose--the first few times he was exposed to nuts (always accidently by someone else), then all of a sudden one day after being exposed he went into anaphylaxis. It is the scariest thing I had ever gone through. Ten days later he had a re-bound reaction. Luckily, his dr. insisted that we always have the Epi and told us "when in doubt, pull it out". So we didn't hesitate to use it. We have heard many stories from other parents that stopped getting the Epi, because of the price & they felt they didn't really need it because it was a "mild" allergy. Other other parents have said that didn't use it soon enough. We were grateful for the education that we received from my son's ped & allergist forewarning us of these issues.
It's all very scary, I know. But it can be managed with your diligence. Check out www.foodallergy.org for a wealth of information.
Good luck!