It sounds as if she is very unsocial and very afraid. #1 . Keep her away from kids. Her fear is stemming from some sort of trauma that she faced in her prior life. Yes...she needs training. She can be rehabilitated.....but you have to be willing to do the work. Bulldogs are such an awesome breed....but they are like small children. They need to be nurtured and supervised at all times.
Others will be along that will have better tips for you. Take care and keep us updated. It will be worth it!