Out of all my leopards, over the years. I have been bitten only 5 times or so. Each one of those times I either got between a gecko and his pinkie or I was doing something stupid like trying to handfeed a hungry gecko. lol. (I now use tongs
) A couple of times they drew a little blood but nothing major. They usually let go right away when they realized whatever was in their mouth wasn't what they wanted. lol.
Just take your time with your sister and talk to her while you are holding the gecko. Let her get used to the gecko being out of the cage. Show her how to hold it and when she gets brave enough, make sure she is sitting on the bed or floor. This is so that if she gets startled and drops the gecko, it won't hurt him.