Am I wrong or ungrateful for being upset about this 😔

I’m 13 and my cousin is 10. We have always been very close and best friends. Whenever my family goes somewhere, we bring her along. And same goes for her family. I will go. I always thought they invited me because I was like an extra member of their family. I got along with all of my other cousins as well and I’m respectful to my aunt and uncle. Well I am on a short vacation with them for the Fourth of July and my friend/cousin was complaining about not wanting to go to the pool. My other aunt wanted to take her and I there. I was all ready to go to the pool and she was telling her mom she doesn’t want to go. Her mom said “go. You’re supposed to be with Hannah (me) for the week. That’s the whole reason we brought her. To keep you busy.” I feel bad because now I feel like they don’t invite me because they like me, but because I keep my cousin out of their hair. I almost feel like it’s a job now and it’s making me upset.