...

] "Her passion for ancient edifices was next in degree to her passion for Henry Tilney..."
..
] "If Henry had been with them indeed! But now she should not know what was picturesque when she saw it."

Well you have chusen your lines well, but I cannot laugh at them. I find the second rather sweet(revealing her by now almost everpresent feelings for young Mr T) and when placed next to the first it makes perfect sense.
Henry is not there so her best loved thing is an ancient edifice. But what good is a garden, a park or a shrubbery if HE is not there to select the outstanding views, comment on lights and shades, give her the best perspective (eh nudge nudge! Which is actually what he has been trying to do since ... since the theatre apology perhaps, when he is convinced there is no evil intended on her part, that she is just a mis-(or un-)guided young woman.)