My sweetest Catherine, how have you been this long age? But I need not ask you, for you look delightfully. You really have done your hair in a more heavenly style than ever; you mischievous creature, do you want to attract everybody? I assure you, my brother is quite in love with you already; and as for Mr. Tilney — but that is a settled thing — even your modesty cannot doubt his attachment now; his coming back to Bath makes it too plain. Oh! What would not I give to see him! I really am quite wild with impatience. My mother says he is the most delightful young man in the world; she saw him this morning, you know; you must introduce him to me. Is he in the house now? Look about, for heaven’s sake! I assure you, I can hardly exist till I see him.” (Ch. 9)

Not forgetting about Isabella’s habit of exaggerating, I have to ask is Isabella interested in Mr. Tilney? It seems her mother might have pointed out he is available and eligible so Isabella wants to check him out. She was willing to chase down the young men from the Pump-room to gain their attention and I think she knew much less about them than she does of Henry. I don’t think the fact Catherine is interested in Henry would bother Isabella and it is obvious she wishes to push Catherine towards her brother. Going after Henry might be killing two birds with one stone.