My blue staffy terrifies people

My blue staffy is 4 tears old,I rescued her from a kennels at 6 months. No idea of her background or how she was kept.she is the most beautiful, sweet and living dog with the loveliest nature. She is excellent with our two young children knows to be careful around them not as boisterous whilst playing etc. However she has this awful habit whilst on walks, if she sees other people she will run off straight away and jumps all over them and you know how high staffies can jump! This really frightens people and she will not come back on her own accord we have to physically get her as she does not leave people alone. If there is no one around during walks she has the most excellent recall!! Really don’t know how to stop her doing this and it’s getting so embarrassing and awful that she can’t be let off around other people. She is the same when we have visitors will physically jump all over them in a real bad manner, she gets so excited at new people but it really scares people! Any advise on why she may do this?? Thanks.