I say: belly button (if it a good/ reactive spot for her- she has a cute tummy)
and a second vote for breasts/nipples (one of my favorite spots to be tickled)
and a vote for hips, since she is showing them off very well in the picture
i say mostly underarms, but all over too! addie you should have her bedspread spread eagle and test all of her spots talking about how ticklish they are like you usually do. F/F please!