Wow. Soooo sorry to hear that happened, must have been very scary. As Lizzie says, take some precautions to get all nuts out of the house and read all labels carefully! I have heard that some doctors are starting to do desensitization with nut allegies but it is very controversial and most doctors won't even attempt it. Maybe over the next decade research and science will make more advancements on it. Yes, you can outgrow allergies, your body cells and chemistry change continuously and about every 7 years or so, people who are allergenic often go through phases of growing into new allergies and out of old ones. However, nuts are such a highly allergenic substance that I would not attempt it or think about it that way - I would plan for her to be 100% NUT FREE for life, unless advised by an allergy specialist when she gets older.
If you should choose the formula route, you would have to make sure to get her a hypoallergenic formula (Alimentum, Nutramigen, Neocate, PeptiJunior, Althera...depending which are available where you live) as she won't be able to have regular formula. To be honest, I would suggest even having a tin of one of them available, just in case something happens again and you realise that you have consumed a nut product by accident and you do NOT want to take the risk in BFing her if her reaction was so severe this time. Again, maybe something to discuss with your doctor.
HTH