They all have their own personalities, some are just more shy than others. This is pretty common behavior for young ones. She is old enough and probably has had enough time to settle in and she is comfortable with her viv. By going into her viv you are intruding on her space. Unlike a dog or cat, the slowly stroking her will do nothing to help settle her. I'd maybe start with putting something small of yours that smells like you in her viv. That way she can take her time, get use to your smell and start accepting your smell as part of her safe place. Then when you do go into her viv just put a flat hand low and in front of her so she can smell you.