i have 7 rats,. I'm 17 i love my rats unconditionally. I clean feed and play with them every weekday and then on weekends i take them to my friends houses in a carry cage.They all have diffen't personallities and some were easier to tame than others, one of my females (SaF) was a shy baby,frightned and always squeaked when i picked her up it took me about 2 months to gain her full trust.I approached slowley and in a calm fashion, don't let your rat know that your affraid be calm and firm at first always put your hand low or flat to the ground she won't be as thretened. rats are curious try waving your finger in front of her or moving things in the cage to catch her attention.Just pick her up don't be affraid she has to learn that it's safe and that you won't hurt her, just put her on your shoulder and walk around don't be to aware that she is there she will feel more comfortable if you do.It's unlikley that once you are holding her in your arms or on your shoulder that she will bite so storke her on the head or rub your finger on her side, it will remind her of her brothers and sisters, once she is interested in you and will sniff your finger try nugging her rats roll around together when they play.
do try letting her run around in a small space where she cant escape like your bathroom sit or lie on the floor were she can approach you and read a book or do something.
try wearing a hooded jumper some of my rats are hood rats they love to hide in the hood of my jumper.
good luck with her let me know how you go