If it was just that Lucy, you'd have a point, but it isn't.
Bridezilla knows how her sister would feel in this position, because she's been there herself, she's done nothing to alleviate the feeling of that. Nothing. She has deemed it acceptable to take advantage of her sister's kind nature though, to get her to organise things on her behalf. How kind. 
She's also been heinously cruel to both her future MIL and her own grandfather, the last of which is completely unforgivable in my eyes.
This is not a case of Annabella feeling left out and throwing her toys out of the pram, it's about the fact that she has a nasty sister who appears to have little compassion for how her selfish actions affect other people, despite having been put through the same herself.
I'd hope that in the light of day (unfortunately this would be after the wedding), Bridezilla would realise how horrible she has been, but the most self-absorbed people rarely do.
Annabella, I'm glad what I've said has been of some value to you. I have family members like your sister so you have my full sympathy. Hope you have a lovely weekend with your DCs. :)