] ...she doesn't even see that until Isabella tells her of the engagement, does she? Could that be further proof that she doesn't see romance unless she's actively looking for it? She seems to see a hint of it with Henry Tilney and herself, or at least to hope that this is what she sees.

...of considering him lost to her for ever, by being married already. ;-)

"Guided only by what was simple and probable"... thus she realises that the elegant lady on Henry's arm is his sister and therefore, "instead of turning of a deathlike paleness, and falling in a fit on Mrs Allen's bosom, Catherine sat erect, in the perfect use of her senses, and with cheeks only a little redder than usual."