Isabella is getting more and more transparent in her false friendship to Catherine, and Catherine does show a sign or two of catching on, but not nearly as often or as clearly as we would like her to.

In Ch. 9 before the drive Isabella says "I have a thousand things to say to you." And in the end, not a word is exchanged between them except Isabella's desolation at not enchanging any.

In Ch. 10 at the theatre that night Isabella swears she will devote herself to Catherine and she teases Catherine about Mr. Tilney, but when Catherine doesn't take the hint and tease her in return about James, "Isabella smiled incredulously and talked the rest of the evening to James."

In Ch. 11 when Catherine is wretched over slighting the Tilneys because John Thorpe kidnapped her and she pours out her woes to Isabella "Catherine could almost have accused Isabella of being wanting in tenderness towards herself and her sorrows...so very inadequate was the comfort she offered."

In Ch. 12 on her way to apologize to Eleanor, Catherine actually takes steps to avoid Isabella!

"...tripping lightly through the church-yard, and resolutely turning away her eyes, that she might not be obliged to see her beloved Isabella and her dear family, who, she had reason to believe, were in a shop hard by."

In Ch. 13 part of the emotional blackmail Isabella uses on Catherine to postpone her walk with Eleanor in favor of the drive is the assertion that Isabella is "her best and oldest friend..." Catherine has known Isabella nine days longer than Eleanor, we're not exactly talking a life-long friendship here, and in fact, Catherine met Henry Tilney the day before she met Isabella.

"Catherine thought this reproach equally strange and unkind...Isabella appeared to her ungenerous and selfish..."

For the first time, Catherine's eyes are beginning to be opened, but all is forgiven and forgotten the next day with the news of the engagement between James and Isabella.