Should I let it go or say something?

My sister-in-law came in from out of town for 2 weeks & is staying half the time with us & have the time with her sister. Before she came to town we found out she had never been to Red Lobster & made plans to take her. She was very excited about it & told her sister we were going to take her at which time her sister invited herself to come with us and also invited their aunt as well. My s-i-l called me & told me about it & said "if the aunt goes I'm not going because she's a bleep bleep bleeping bleep". After juggling schedules & re-arranging plans, we finally decided on a day & time to go (which was planned to be this coming Friday).

Yesterday, after my s-i-l knew that I had already started dinner, she pops in & tells me she, her sister & the aunt are going to Red Lobster in an hour & asked if we wanted to come with her. Well, of course we don't because 1- I've already started dinner, and 2- my husband won't even be home from work yet by the time they leave to head that way.

So basically, A & B make plans. B tells C & C invites herself & D. B says I'm not going if D goes. Then B, C & D get together & plan to go when they know good & well that A can't go, therefore leaving A out of her own plans.

I am extremely ticked off - and hurt - by this. I know I should just let it go & not rock the boat, but I really want to just go off on them about it.

So, should I let it go or say something?