Inside Mary's Bedroom
Mary's bedroom is located in Room 15 in the Men of Letters Bunker. She's only just joined her boys at the bunker, so she doesn't have a lot in her room yet. We can see she has some boots and clothes on a chest by the door. Nearby, she also has the same standard heater in her room, as well as a floor lamp. On the desk there is a small mirror and some various bottled lotions and creams. There is also a black notebook and pen, as well as the standard black rotary phone that appears in the other bedrooms. She has a second chair in her room, which has a red sweater draped over it in 12.02 Mamma Mia. Her room has the same sink and mirror near the door that Sam and Dean's rooms have as well.
People who have been in Mary's room:
At the end of the episode, Sam goes to Mary's room to bring her tea. Mary is sitting, quietly brushing her hair at the desk, when we first see her. Sam seems nervous and rambles a little. He tells her he's available to talk, if she needs to, about coming back and not fitting in. She replies that she has a lot of "mother stuff" to catch up on. When she says there are a lot of blanks to fill, Sam gives her John's Journal to read. She thanks him and he says goodnight, turning to leave. She stops him and says that Dean told her he got out of hunting. He explains this is his family, it's what they do. He says that having her there fills in the biggest blank. They hug.
When Sam and Dean figure out a way to save Kelly Kline and her child, Dean goes to Mary's room to retrieve Castiel, only to find him missing. This suggests perhaps Room 15 may be used as a guest room.