Mary's room seems to be arguing that,

[experiencing(red)] =/= [experiencing(understanding([experiencing(red)] )] )]

(translation: the experience of seeing red is no the experience of understanding how seeing red works)

This is true, when we take those statements literally. But it's true in the same sense a Gödel encoding of statement in PA is not literally that statement. It is just a representation, but the representation is exactly homomorphic to its referent. Mary's representation of reality is presumed complete ex hypothesi, therefore she will understand exactly what will happen in her brain after seeing color, and that is exactly what happens.

You wouldn't call a statement of PA that isn't a literally a Gödel encoding of a statement (for some fixed encoding) a non-mathematical statement. For one, because that statement has a Gödel encoding by necessity. But more importantly, even though the statement technically isn't literally a Gödel-encoding, it's still mathematical, regardless.

Mary's know how she will respond to learning what red is like. Mary knows how others will respond. This exhausts the space of possible predictions that could be made on behalf of this subjective knowledge, and it can be done without it.

what Mary doesnt know must be subjective, if there is something Mary doesn't know. So the eventual point s that there s more to knowledge than objective knowledge.

Tangentially to this discussion, but I don't think that is a wise way of labeling that knowledge.

Suppose Mary has enough information to predict her own behavior. Suppose she predicts she will do x. Could she not, upon deducing that fact, decide to not do x?

Mary has all objective knowledge, but certain facts about her own future behavior must escape her, because any certainty could trivially be negated.