You put the key in the lock and unlock the door. Entering, you see a queen sized bed with a somewhat sloppy top blanket. At least the bed has sheets and is kinda made. There is a corner filled with stuffed animals. Take a look?

You go through some of the stuffed animals and plushies. Most of them are pretty random and stupid. One had a card attached to it. It says, "Heya Frisk! I knew you'd get in here eventually. Welcome to my room. This is for you. Also please give Sans back the key you used to get in here. It makes him feel better." The plushie is of Flowey. You put it in your bag.

There's a dresser cluttered with random assorted objects, including a spiked collar and lead? You decide to ignore that for now.

You walk over to her closet. It has a few dresses hanging in it. There's a Blanket on the bottom of the closet that you've seen Doki wrapped up in a few times, but other than that, nothing of interest really.

You leave, and run into Sans again. You give him the key and walk away.