"...obvious that Isabella fell "head-over-ears" in love with Captain Tilney..."

I don't think that is obvious at all. I think she was DEEPLY flattered that such a rich, handsome, man-of-the-world seemed to want her, but I don't think she FELL IN LOVE with him. Do you see it in the text? I wouldn't be surprised if I missed it.

"She is so obviously over James."

I don't think that is correct, either. She knows that she blew it with James, and, having lost the bigger prize, Capt. Tilney, she wants James back. I think she has convinced herself that she still loves James (as much as she is able to love anyone but herself), and that is why she wears his favorite color: to please him, even though he's not there to see it. I don't think she's insulting his taste, she thinks she's showing her GREAT love for him! It's a feeble attempt at reconciliation, a last-ditch effort.