thanks.
Still can't work out how it happened. She wasn't part of the group or anything, she was just there.
@Vesper I find this happening to me, too, when traveling to Granite Falls or Selvadorada.
Though I specify an adult sim to go alone, leaving the children behind with other adults in the household, the game will go ahead and invite along other household members on its own.
I once redid the Take a vacation... command 4-5 times but it kept happening.
In the end, I just took all the darned sims to Granite Falls then sent home the ones I didn't want there.
In your case, it's trickier because the game didn't even show you who would be traveling with your sim.
Anyway, I'm just posting to commiserate and to say I'm glad you're allowed to take a point loss rather than failing your challenge.
Still an annoying bug, though, eh?