NORMAL PITBULL BEHAVIOUR?

i have a 1 yr old pitbull whos always been very affectionate and playful. lately though a few things have happened that are starting to worry me ... before when i would walk her and she would meet another dog she would whine until i let her go over to sniff the other dog and she would just wag her tail n try to play. lately tho, when she sees another dog she starts barking and growling at them but still waggin her tail and whining, the other dogs get terrified and then everyones barking and pulling...she also snapped her jaws and growled at a stranger who tried to pet her..and shes growled at two other people passing by. she always barks and growls at my brother for some reason but in the same wag tail/ whining kind of way.. and she once growled at my mom for trying to push our chihuahua off the couch (she adores the chihuahua) she also tries to run out the door everytime she gets a chance and wont listen when i call her to come back like she used to. is this normal behaviour because shes getting older? should i take her to those training classes?