What's it like to have a sister-in-law who is only a few years old?

My family has a little sister-in-law, ten years younger. At best, she is simple and spoiled by her in-laws, at worst, she is stupid and heartless. As long as she eats, drinks and dresses well, regardless of other people's lives, she 16 years old when I was born and cried several times because my mother-in-law took care of my confinement and ignored her. I had a caesarean section, and my baby was big and the wound was big. I want to sleep every day. My mother-in-law is very kind and hard-working, but only if she doesn't provoke other people's daughters. Anyway, as long as she won't let me wait on her, my husband won't spoil her because she has a sister. My husband has been a left-behind child for four years, and my sister-in-law takes him everywhere. It's not nice to say that brothers and sisters don't kiss. When she came back at the age of three or four, she didn't even know she had a brother. Another advantage is that her sister-in-law never touches my things or pesters my husband. Besides, my husband has never washed socks or dishes in high school, and he just learned to deliver meals recently. In rural areas, in-laws have no pension, worked all their lives and can't afford to buy a house. My mother advised me to think clearly at that time. My husband is very kind to me, but he feels a lot of pressure, raising children and buying a house for boys. At that time, he had no hope of supporting his in-laws and sister-in-law. My in-laws also said they didn't know what to do. Sister-in-law needs money to go to college. If she changes, it doesn't matter, don't wait!