Supposes its how do you mean nasty to strangers?
Have you ever seen The dog whisperer or dog borstal? there is some good advise given and tips to be picked up.
Dog Whisperer: National Geographic Channel
BBC - BBC THREE - Dog Borstal
IMO a training lesson/s is all good but the basics can be learnt from a little research as the main principal is that she will have to do the training.
Dog lessons can be expensive.
Google is your friend.
