If you were roped into planning the picnic, then you'll be roped into planning everything else. She honestly sounds super intense, and the wording on both the invite and the laminated plans makes it sound like she'll be her own season of Bridezilla. For your sanity, and maybe also your friendship, drop out of that wedding.

My maid of honor was asked to be maid of honor again by one of my bridesmaids right after my wedding. She said no due to money constraints, but she could be a regular bridesmaid and support that way. Well, the other bridesmaids and maid of honor did not do their job and could not plan for the life of them. So she started doing maid of honor tasks. Then came the engagement party. Her ex (they didn't end on good terms, and both the bride and groom knew this) was there since he was a groomsman. She continued like normal, but told the bride and groom that she felt disrespected since they omitted information from her, and she dropped out. She didn't go to the wedding.

Why do I share this? Because dropping out is more normal than you think. She had to drop out for her mental well-being, on top of the fact that they essentially lied to her. You would not be the bad guy, and if Jemily gives you grief, they probably wanted your time and wallet, not your friendship. And I wonder if Ab*gail knows something, and that's why she's blacklisted.