Pretend this is written on an Rx bottle. Thus,
"Whatever you do, do NOT enable or encourage this self-absorbed she-devil's demands on your time and money. She is toxic and will continue to demand more of you. Run, don't walk, away from her."
Like so many today, she's obviously putting more money, energy, thought, preparation and desire into the wedding...and ignoring the marriage. We can speculate how that will unfold in 6 months.
If you're concerned that there may be repercussions at work if you do not bow to her extortionist behavior, write up something documenting the invite, her demands, and anything else you want add and make a copy. Put both into sealed envelopes. Keep one at work and mail the other to your home address. Do not open the one sent to your home, just tuck it away. It will have a date on it via the post mark. Then, if you have any problems with her and you believe it's because of fall-out from this extornist scheme she's inflicting on everyone, you will have something to back up your response. The post mark will show that you "didn't make this up last night."
Do NOT be sucker-punched into giving in to her!!!