Fear biting

Question
I have a three year old sheltie that I fostered for a sheltie rescue group I volunteered with.  She was given up for being "overprotective".  She bit a neighbor - did not break the skin, but did leave a mark.  This neighbor has some health issues so her skin is not what one would consider normal. She is trying to be kind and understanding, but this dog is out of my range of expertise, and I would love to be able to get her to where she is able to behave herself and be a good citizen, but I fear I may not be able to help her much more.  I don't know how you feel about the methods Cesar Melan (The Dog Whisperer) uses, but I have used some of his techniques. They have helped somewhat, but like I said I feel i just do not have the training or expertise to do her much good.  I did take her to a class about a year ago, but the techniques I learned there have not helped much.  your advise please!!!!

Answer
Well what you can try is to have strangers(friends of yours that she doesn't know well would be good)give her a little treat while they are petting her,another good idea would be to have someone pet her at the same time as you,and gradualy stop petting her while letting the other person continue petting her