The TARDIS transmits a message that could probably most accurately be conveyed as: "That's stupid."

Sure, Rin's* probably not what the humans would define as a person. But their definitions of things like "life" and "identity" and "sentience" are narrow and misguided. A sadness at a lack of identity is just not something the TARDIS understands, as she is very certain in her identity. And maybe she thinks Rin's a little silly for worrying about it.

*'Rin' is stand-in for the feed address.