Oh wow, that's a tough one! My deepest sympathies. I think both ideas are good - I also think though that both could be taken the wrong way... such as "oh, this is so depressing" or "oh, I can't believe that she'd replace her". Still, if I 'd have to make a choice, I'd probably go with honouring her with a memorial. Weddings are supposed to be happy, a celebration of joy. Such a hard decision... Best of luck with it!