People associate wagging tails with friendly dogs, thats not always the case. A dog can still be wagging its tail while biting your arm off. If the tail is held high and wagging stiffly, this is usually a sign of aggression. If its friendly wagging whilest barking i would think she's just warning them off her property but maybe still wants to be friends. Without seeing it its difficult to say. My dog is highly socialised and interacts with dogs all day every day but she'll still bark when dogs go past the gate, its her territory. Have you got any friends with dogs you could walk with for a start? If she's not showing signs of aggression, get her off lead and playing. Being on the lead can also make some dogs aggressive to others :-)