How do I teach my dog to stick up for itself?

My dog is now 2 years old and she is a Jack Russell Terrier. However not like any other jack russel mine is an absolute wimp, she runs away from ALL other dogs, even if they are puppies, scared after every flinch of your hand, (by the way we have never hit her), wee's herself when you raise your voice and is summed up, a little wuss. Is their any tricks to toughen up your dog or allow her to stick up for herself because it is quite embarrasing.

She sounds like she's very submissive. She might just need a confidence boost. Enroll her in an obedience class with a trainer who specializes in shy or submissive dogs. She might just need help coming out of her shell.