I don’t like it when my sister changes the plan last minute

There’s this pattern with my sister. She often comes in last minute with an idea or situation – OR she makes plans with herself or her husband about things which involve other people and only lets me in on it last minute. For example, It has happened when she wants help with the kids – she asks my mom if the kids can stay over for the weekend and my mom agrees and then she lets me know the day before (I live close to my mom with my daughter and my sister lives further away), knowing that I would step in and help my mom because it’s hard for her to take care of 3 small children by herself. Plus, my daughter, is the same age is the oldest and they are very close.
I would do it and get mad while doing it. .. and then I listened to Brooke’s podcast on boundaries and started speaking up about it – and said..” You have to tell me ahead of time if you are going to leave the kids here, otherwise, i’m not going to help..don’t assume I will drop my life and help..” and of course, I had to follow through and felt like a jerk when one day, for example, she dropped the kids off and didn’t tell me ahead of time, and I separate myself and my daughter from the situation…I felt badly because my daughter wanted me to take all the kids to the park, for example… but I stood my ground and my sister started ‘asking me if it will be ok if…”

And now, another situation came up where we (my daughter and I) are supposed to go down this week for the holiday to my sister’s shore house – we have been planning this for at least 2.5 months (i’m a planner) and today, on a phone conversation as a ‘by the way’, she told me that on the days we will be there besides the 4th, she is sending the kids to camp! HUH? Why would I agree to make these plans if my daughter won’t be able to hang out with her cousins? again…. last minute… I mean, I enjoy my sister, but I could have planned different activities for us to do together with other kids involved! I am feeling very angry and annoyed and need help modeling this out, because I can’t seem to get my emotions in order – I just want to be right, but I know that isn’t serving me.
Here is my model:
C: Sister
T: ugh. She is doing it again, letting me in on her plans last minute. I don’t like it when plans change last minute and she doesn’t fill me in ahead of time. I’m not going to go down the shore, i’ll show her what I mean about changing plans without notice.
F: Disrespected
A: Texting annoyed / angry texts back and forth
R: We will go down the shore and the girls will not go to camp only 1 day. I will be annoyed.

C: Sister
F: Unconditional Love
A: Just saying once that I will not come unless the girls stay home form camp. Ending it there, no need to text back and forth.
R: Go / not go / doesn’t really matter…

Thank you so much!