I've just looked at your other posts and see that she's just coming to the end of her first season. That means she's been going through some very big changes over the last few weeks. Puppies often go through a second fear stage between 6 and 12 months so I expect that combined with her season are the cause of her becoming timid. If she was mine and backing away when people approach I wouldn't let them approach her for the time being because it may increase her fear.
In one of your other posts you say she's always sniffing her vulva. Did that start at the same time as the generalised scratching and nibbling? Scratching and nibbling could be due to any number of things including fleas, skin mites, food that doesn't suit (as an example, grains, especially wheat, are a fairly common cause of skin problems) or environmental causes. Some dogs can be very sensitive to laundry products used on their bedding, carpet and floor cleaners that they come into contact with in the house etc.