Guinea pigs are prey animals in the wild, so being skiddish is normal behavior for them. Some pigs will tame more than others depending on their personality, environment, and how much they are handled. It takes time and patience. I have 6 pigs that I have been working on taming for 6 mths-1 yr. Most of them are pretty tame--are willing to approach me, tolerate being handled, and are comfortable enough in my noisy home to lay out in the open of their cage. A couple of them are much more skiddish than they are tame. They will reluctantly and cautiously approach me long enough to snatch a veggie and run, and will occasionally tolerate handling, but for the most part they still pretty skiddish and some of the slightest of things can send them frenzying for a hidey house.
Good rules of thumb to help tame them down:
-Don't expect too much too fast. It takes time to build their trust.
-Don't keep things too quiet in their environment. In my experience most of them adapt very well with the sounds of the household if given the chance. If they are never exposed to different sounds, then they fear all sounds.
-Plenty of hidey spaces. While your pig is adapting to her new home be sure to provide plenty of places for her to duck into quickly when she feels afraid. Being able to "hide" is their security and in turn boosts their confidence in exploring their habitat. Several small boxes with two entrances in them, or large pieces of PVC placed about are a good way to do this.
-Treats, treats, and more treats. The fastest way to a pigs heart is through it's stomach! Nothing makes them happier than leafy greens. It may take many failed attempts to coax your piggy to approach that veggie in your hand, but try try again...Eventually she will brave it and it is an immediate bond with you. Approach her cage several times each day and just hold out something for her to take from you and talk to her in a calming voice. Don't attempt to grab her, just allow her to build confidence approaching you.
Have you considered a buddy for your girl? Pigs are social animals and are happier, healthier, and more confident when in pairs+.
http://www.cavyspirit.com/sociallife.htm
Guinea Lynx :: A Medical and Care Guide for Your Guinea Pig