How can I get my friend's baby niece to stop being scared of me?

i would go to the babies house and try to spend large chunks of time with her. maybe ask if you can babysit. it might be that the babys still not used to you. during those times, do some exploring to see what works. see what the baby responds to and considers fun. then do those things with her. she will start ociating the fun things with you, and the relationship should improve.