So, here's the wishy-washy perspective:
Try talking to your DSD?
Not disciplining, not getting DH to do it - you're pissed off because you don't know what's going on, you've tried to make an intervention through DH, and it hasn't worked, and you're confused about why. You don't understand what DSD is up to, i.e. taking make up when she has her own, daubing it on the walls etc, and it's frustrating
So ask her - preferably in a nice setting, where you can really listen to her answer. It will also give you a chance to explain to her why the items are important to you, how the situation makes you feel, and get a firm commitment from her not to do it again. If she goes back on that, you'll at least know that she knows what she's doing is wrong, by her own standards.
As for the OP question 'Am I being unreasonable' - no, not really, not at this stage. Taking the commitment to making a family, navigating the feelings involved, learning to live together etc, these things are all super difficult, for you and for her. Janky situations are always going to pop up. There's a reasonable slice of the posts above that boil down to 'I'd get cross and leave' and that's fine, we all get to choose our path, but that ultimately represents (literally) an inability to live together.
Based on the ages of your respective kids, and the fact that you've still got make up from back-when, this is quite possibly the first time you've tried to navigate a living situation like this. It's normal and reasonable to feel frustrated.
But you're an adult, you've taken on a responsibility to live with and provide care for a child. If you strive to treat all the kids equally, then think how you would address it in the first instance if it was your DD doing this. And no it may be that your DD would never take anything without asking, but believe me, there is some janky, baffling unexpected behaviour coming down the track from DD too. If there's any part of your brain that harbours doubts that DSD is just different, because she's not like you, because she's not related by blood, you need to address that pronto because that's not a fair way to treat a child.
No doubt your property needs to be respected, and definitely there's some parenting involved in fixing that, but it's also worth reflecting on whether the situation might offer the opportunity for growth for you too.
Anyway - hope it all turns out for the best whatever you choose ✌️