Well is it better to bring her or leave her at home if she doesn't want to go? She may prefer to stay home with the kids... which would save on babysitter costs...
To me, this sounds like a scenario where I would let go of being tied to any particular outcome on her end.
Can you act based on your own values, and allow her to make her own choices, and not get too tied up in hoping/wanting/convincing her to do stuff?
It might look like inviting her, and then accepting that she may come along, or she may at the last minute not, or she may do or say any number of weird, fluctuating things leading up to the trip.
Instead of "giving weight" to each and every thing she says and does leading up to the trip, I wonder how it'd go if you accept that that's how she does life -- she might be absolutely certain on Tuesday that she's going, then on Wednesday be absolutely certain she's staying home, then, 5 minutes before you get in the car, decide to come along.
Maybe consider not arguing with/trying to convince her of "what she should do". Announce "hey, the reunion is next month on Day/Date -- I'd love it if you came along!" and let her do her process of having different things she's absolutely sure of based on how she's feeling on any particular day. Know that it may come down to the wire, so if there are things you have to do "on the side" to make it happen
for you, do that -- i.e., letting a sitter know "can you be on standby on Day/Date? We may need a sitter for 36 hours but we won't know until day of."
Invite her, enjoy it if she comes along, accept if she makes her own choice not to. No pressure. Get your own ducks in a row in the background to facilitate your trip, no matter what she decides.
That's sort of how I'd approach it, where her accompanying you or not isn't a "make it or break it" part of the trip and won't derail you from going either way.
Make sense?
