Mom Not Invited to go to the Zoo

My MIL told me a couple of days ago she wants to take my 2 year old to the zoo next week. 2 weeks ago I wanted to do that as a family but didn’t make it. Anyway, she didn’t give me any details, or an actual timeline. Today she asked me if she could pick her up at 9:30am. I said ok to that then my husband asks who is going and it was going to be my SIL with her 2 kids and another family member. Now thinking about it, I wasn’t invited and she wouldn’t tell me any details because she didn’t want to tell my SIL was going, since we’re at odds and probably doesn’t want me there. I think it’s very sneaky and rude. There are 2 options I could approach this. 1. Ask my MIL about their Itinerary and say I want to join in because these are first time experiences I want to do with LO (which is the truth)

2. Tell my MIL I have decided for LO not to join because I want this to be our first zoo trip as a family.