She needs to let go of the idea of being her stepdaughter’s «new mom.»

It’s all too common for children and teenagers not to be treated like whole human beings. I’m not saying that 12-year-olds should be able to vote or drive a car, but they should be afforded the same empathy and dignity that you would afford literally any adult. You shouldn’t deprive them of their right to privacy by unscrewing their bedroom door. It’s wrong to take things that belong to them and give them away without asking, even if you, as the parent, see it as «your property» because you bought it. 

Parents often do questionable things in the name of discipline that they wouldn’t expect of an adult. They might send their child to bed without dinner if the child refuses to eat what’s made for them. You wouldn’t do that to an adult who doesn’t eat what’s served to them at a dinner party. Most adults wouldn’t refuse a meal that’s made for them because they were taught at a young age that it’s bad manners to do so. But even if an adult did that, they have the autonomy to make themselves dinner when they get home, whereas a kid doesn’t always have that kind of liberty.