You have a little baby that is in a strange house with a strange person and three weeks is way too soon. I know you say that she allows you to touch her everywhere (even in places where you should never touch a parrot, mind you) but all babies do that and it doesn't really mean she has bonded to you. You need to be patient and spend a lot of time with her and not necessarily touching her all over (Grays are not big on having their body touched unless they are hormonal so it might be this handling that is preventing her from giving you her complete trust). She is also way too young to start training her to target (this is a baby!). Offer her soft foods twice daily and make sure you 'eat' with her. Spend time just chilling together (you can put her on your lap while you watch TV or whatever). Give her a treat or two when she is with you -not as a reward for doing anything but just as a way of showing her that you love her and want to be her friend. And, offer her your open hand for her to step up (palm up) and see if she does it -she is very young and might feel not too sure of perching on a finger or edge of hand.