Well, first of all, and I can think of no polite way to put this, your vet is an idiot!! The window for socializing puppies closes at 16 weeks, that's four months old. After that it's a long drawn out, slow, limited process!! You shouldn't have taken her to dog parks and places where you couldn't guarentee the health of other dogs, but she should have met other dogs who you knew had their shots. She should have been exposed to as many people, places and different things as possible long before now. Socializing her can be done at any age, but it's much harder and takes much longer now.

Dog aggression is a JRT trait. People aggression is not. They are assertive, dominate little dogs though and require consistent, firm but gentle handling. They are hunting dogs. They were bred to hunt and work. They need mental and physical stimulation in large amounts! If your dog can't be walked even, she is getting neither and the problem will only get worse. A bored dog of any breed is going to get into trouble!

Get her to a trainer who specializes in aggressive dogs--a good trainer. Do some research on the trainer before taking her to anyone. You said she bites people when they try to restrain her? All it takes is one bite to a child or anyone else that gets reported to the authorities and your dog is dead!

http://www.terrier.com/breed/breedmenu.php3

Maybe there is a JRT club or other owners in your area. They could likely point you in the right direction for a trainer.