I don't think you're a bad mom. Having respect for the things of the people you live with will go far beyond living with you in your house. It is something she will need to learn when living with anyone. Her future roommate, spouse, and children will all deserve the same respect of their things as she gives you.

So, I think you're both just at a point of tension. I think it happens with kids and parents sometimes. Instead of resolving the problem you've both gotten to a point where it stagnated. She is feeling like she's ready to be grown-up and on her own. You're at a point where you have just dealt with it for so long you're aggrivated.

Don't take this personally. She's trying to spread her wings before jumping out of the nest. I think it's a normal thing. It's an age thing. I bet things will turn around in time. For now, though, give her more and more responsability since she's going to move out. Tell her that, since she is preparing to move out that she needs practice. When you get into arguments, have a point set in your mind that you won't go passed in your anger and walk away from the argument.

I have some explosive anger and setting up a point in my mind before arguments even happen has been helping me. Walk away, go do something distracting, and fight every urge to escalate the fight.

And, your daughter still loves you, you're just in a tense spot right now. I had a similar thing with my dad. We do better living in separate homes than together.