In the asylum you can find a inflated rubber ducky tube. As you are walking around on top of the asylum you will see the lady in the icon standing there talking about the moon, a sticker can be placed on her waist.
You should use the rubber ducky tube on her and she will thank you, and this trophy unlocks.
This is not required for the main story, however you can always chapter select to return to this stage if you missed it.