She says there are seven tiles. You can see five of them. There are only so many spots they can be hidden by her belly. As a hint, every tile is at least diagonally connected to each other.
I've been trying every combination of two in the four spots her belly hides but it's not doing the trick for me. Is there something I have to press to confirm my answer or does it just automatically trigger the completion even once I light up the correct ones?