You should take her shopping and buy her expensive skincare and give her your bedroom and en suite OP.
Once you have kids you aren’t allowed anything for yourself or to have your own space and as for step kids… well you knew your DH had kids when you married him and that means they can do whatever they want and you can never ever complain.
It doesn’t matter that you work hard and have to make sacrifices and are just trying to put some boundaries in place - kids are entitled to everything they want and if they help themselves to your stuff without asking then the obvious solution is to reward them by taking them out shopping for expensive skincare.
I’m in therapy because I grew up conditioned to always “be kind” and ended up being a complete pushover with everyone and terrified of conflict. It didn’t matter how much someone treated me like shit I’d just take it with a smile.
I realised it’s not a healthy way to be far too late and after years of being taken advantage of and it frustrates me so much on threads where posters go on about “being kind” when someone is being used, having boundaries trampled over or in any situation where they should be standing up for themselves and not appeasing the other party.
I don’t know if it’s just people being contrary for the sake of the thread or if they mean it but I actually think being advised to “be kind” when it sacrifices your self respect, boundaries or your own feelings is harmful advice and I’m always relieved when it’s a minority opinion that’s criticised.
Threads similar to this also show why so many kids grow up to be so entitled when they get given anything they want because of their age and because they are “just kids”.
I agree with the pp who said it would be a different story if OP was the one going into her stepdaughters room and stealing her belongings and ignoring the fact she’d been requested not to go into her space.
I understand your anger OP and I’d be as outraged and pissed off as you are. It’s a shitty move of your stepdaughters likely done to deliberately disrespect your wishes and knowing her dad won’t back you up - it’s a power move.
I hope you put yourself and your DD first and move out into your own house where you aren’t subsidising people who don’t deserve it, I bet you’d be so much happier.
I’ve read lots of threads over the years I’ve been on here from women who are treated like shit by their DH and his kids and are almost always the highest earners who own (or paid the majority for it) the house and are still expected to be a nanny with a fanny and housekeeper.
The ones who had enough and moved out updated saying how happy they were and how much their lives improved, I hope to read an update one day from you saying the same.