Make her bigger, M-cups or so, and listen through the door.

You check around the hall, verify no one is coming and pull out the notebook. You want her bigger but maybe not so big she'll be immobile. The letter M comes to mind, so you start to write. Then, you get a passing thought.

What happens if you're a bit more specific?

There were a few rules mentioned. You can't write guy's names... including your own presumably, but you CAN use titles. You're her neighbor so... you write a story.

After chatting with her Neighbor, Shannon returns to her room to suddenly start growing. Her breasts swell up to Natural M cups, busting out of her t-shirt.

You feel stupid as soon as you finish writing. There's no way something like that could happen. You don't even have a cause. Boobs don't just randomly--

The text turns red.

You hear a surprised yelp behind the door, and the sound of someone falling over and the clatter of objects collapsing to the floor.

Did it work? You check the door, realizing she kept it unlocked. You could check on her.