Is this the first time we get an explicit message in the book that Fanny has an "guarded heart" and already "engaged affections"?

Ch 24: And without attempting any farther remonstrance, she left Fanny to her fate, a fate which, had not Fanny’s heart been guarded in a way unsuspected by Miss Crawford, might have been a little harder than she deserved; for although there doubtless are such unconquerable young ladies of eighteen (or one should not read about them) as are never to be persuaded into love against their judgment by all that talent, manner, attention, and flattery can do, I have no inclination to believe Fanny one of them, or to think that with so much tenderness of disposition, and so much taste as belonged to her, she could have escaped heart–whole from the courtship (though the courtship only of a fortnight) of such a man as Crawford, in spite of there being some previous ill opinion of him to be overcome, had not her affection been engaged elsewhere.