Ruby was a demon devoted to Lucifer's return. After Azazel's death, she conspired with Lilith as to how they would free Lucifer from his cage: while Lilith broke the seals, Ruby protected the remaining "special child" you, and prepared you to break the final seal and become the host to Lucifer. This plan was known only to herself and Lilith.

You were asleep in your motel room, Ruby teleported silently into your room.

”The special child…he’s so cute when he’s sleeping..”