The big wedding and expensive ring was never my idea of fun. My own wedding was registry office, dinner with 20 friends and family, the whole thing including outfits and rings cost less than £800 (in 2002). I wonder if Helen's first wedding was a small affair and she fancied treating herself to the whole shebang? I could understand that if she'd always dreamed of a big day and hadn't had it before? (ETA: Seen post above that she didn't want a big wedding, so even more confused now!)
That said, you would surely realise if you were organising it late and somewhat on the hoof that big venues are not going to be easy to secure and they'd even possibly be relying on cancellations? I think she'd be quite practically minded about that, and I don't think she'd be terribly upset about it as IS has constantly made out to people.
I've found that men like IS love to demonise the woman in their lives, make them out to have all sorts of faults and weaknesses, so when the inevitable split comes they end up smelling of roses.