I agree with the others. Shes probably seeing things everywhere that look SO COOL and wants it all to fit in her wedding. Im helping my soon to be SIL with her wedding. Im baking the cakes but Im also helping make decorations and doing the set-up of the tables and decorating them too. Her theme hasnt changed but the cake design has changed more time than I can count and everyday that I talk to her shes had a friend show her this or she saw that online etc etc. Even though my bride is my soon to be SIL and my cake is a gift I still kept my mouth shut when she picked out some really horrid designs. It's her cake and her special day. I'm not a bakery owner or a pro so I don't have a reputation to protect. If I did I might handle it differently.
When my best friend got married she went all wedding crazy too. In the end she settled on an autumn theme, oranges, reds and browns and yellows, lots of leaves, pumpkins, mums, hay bales etc. So Im helping set up the foyer of the church, bucking bales and stacking potted mums and scattering leaves around when this group of guys show up with a HUGE white arch decorated with green ivy. I had NO IDEA where it was supposed to go so I told them to sit it over there and they left. Not too long after that a big delivery truck showed up with a bunch of tall Ionic pillars. I had them sit them with the arch. They told me they had another truck coming with the rest of the order, more pillars in differing heights. I went to get my friend. She looked around at the arch and pillars and had no idea where any of that had come from. She couldnt remember ever ordering it but the delivery people left receipts behind so shed paid for them at some point. So we staged the pillars with mums and tried our best to make everything fit in with the final theme. And sure enough as soon as we walked out into the foyer there was another delivery of potted plants (this time a bunch of lilies and ferns) from a florist that she couldnt remember visiting lol. The arch was used as a prop for guest to have their pictures taken under (which turned out REALLY cute). My friend had so many potted flowers we were stacking them in any free corner of the reception hall and the sanctuary.
I guess at some point her theme was something else and she just impulsively bought stuff to go along with it and forgot (she had been planning the wedding for almost a year). Its a funny story now though lol.