In my experience with rescuing ferals, (my aunt owns a feral rescue) some can indeed warm up and do an about face, but it's rare, and most do not. They are, for all intents and purposes, wild animals.
It may be best to allow her to be an outdoor cat. Although this means, annual vet check ups, extra vaccinations, making sure she is micro chipped, licenced according to your city by-laws, has a collar with tags, and that you have some money put aside in case of unexpected vet visits from accidents and injuries.
...That being said, in the end, you have to do whats best for your family, both furry, feathered and otherwise.