Fear - Bailey

I did not think i would be having fear issue but here it is....

just discovered that my dog is fear aggressive towards: skinny, tall guys  (discovered this at SAR training/introduction/orientation on Saturday)....WTF? it was the worst time for her to show that......never had issues with her...she has been everywhere with me,  kids can approach, women, chunky man - no problem what so ever...but tall skinny man and she becomes a fear biter (two man at the training were disliked by her as soon as they approached, ears back, tail straight, feet wide apart, whites in her eyes and she kind of lunges towards stretched out hand)...has not bit yet...i am just taken back...and very surprised (mildly put)....

k-9 handler on site said she is scared of these type of man, and not to correct her because if she is corrected when i can tell she is getting nervous she will know not to show her fear but lunge and bite without warning....

since this is my first time dealing with fear biter who is also handler sensitive (which i can and been working with), and i guess somewhat nervous dog in new areas/locations, where should i start? any suggestions?..more exposure to public?

few key points...she is okay in crowds, down towns, around people, in stores, around most dogs, around kids, good with women....it looks like once someone focuses on her and come up face to face with only 2-3 people around she gets nervous, direct eye contact with a stranger makes her unsure, with me and anyone she knows she has no issues with eye contact and holds eye contact very well...if she approaches them (strangers) she is okay ...tail wag, sniff, not totally comfortable, little shy but still comes forward and greets....

also, I been warned by a vet that her being in constant even low level of pain would make her self consious or nervous...could that be true? but than why is it selective few not every stranger?....

I swear this dog will be the death of me she is like a treasure chest of bad surprises...between health issues, personality and now temperament...