"Oh, yes."

Here in her pocket is the key to her Milliways room. She didn't keep a key to her father's house with her -- it never occurred to her that she might need it unexpectedly -- but Milliways shows up at the strangest times, after all. She passes it over to Marius, and tells him the room number, which is stamped on the key too.

"You see how these doors all have the numbers. That is mine, so of course it's yours as well. I'll go there as soon as I'm done speaking with Mother."