Is my sister being manipulated, or does she choose to accompany her husband?

I know that when you are married, many things you do it as a couple but in order to have a good relationship you also need indpendence, that means doing things without the other one. Things you do as a couple visit each other in laws, but also you can visit them without the other one I mean you can visit your folks and not necessariy you have to bring your SO right? My brother believes our brother in law manipulates oru sister. Because she has to go with the husband to every single activity he goes or is invited, I mean activities thath y brotehr in law can go by himself, but he gets my sister to always accompany him. For example, my brother in law has his mom in a nursing home like 2 years ago. He goes to visit her on Sundays and feed her. After he visits his mom, he takes his dad to lunch, and that is a habit each Sunday: Visit his mom and takes his dad to eat lunch. My sister always accompany him to do these things, she goes to visit her mother in law and goes with his dad in law for lunch as well each Sunday. I mean my sister has not stopped doing that since her mom in law is in that nursing home. But then sometimes when my brother and I organize something like a get together on Sunday and we invite our sister and the brother in law in the afternoon, she always said she can't because she has to go to visit her mom in law with the husband and then eat lunch with the husband father. I mean my sister never had skipped a visit to see her mother in law and I beleive if she skips one day nothing will happen. Her husband can go on his own and then take his father to lunch, my sister not always has to be there with him. After my sister visiti her inlawas she always visit our mom at the house, it is like a routine now. First the in laws, then our mom.

My brother believes our sister is being manipulated because she does everything her husband ask her to do and she can't say "No" to him since they do many things together as a couple. I mean my sister could

Updates
14 d
easily say to the hubbie: "Today I be going to my sibling event you can go on your own to your folks" This is not the first time a smiliar thing happen with my sister and her husband when we tell her to come or we tell her to invite her for something. For instance, my sister husbadn has 3 kids from aprevious marraige and he is already a grandfather. My sister gets along very very well with her husband kids.
Updates
14 d
My sister gets along very very well with her husband kids. My sister had skipped some family events because she goes to birthdays of her husband granddaughter, beacuse her hubbie ask her to go and join him.
Is my sister being manipulated, or does she choose to accompany her husband?
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