Step daughter taking my clothes and claiming it is hers.

I am at a loss on what to do about this. It seems so petty and futile to even find a resolution in this area but it just keeps coming up.We are currently on a trip visiting family. I was getting dressed this morning and was looking for a pair of my pants and found them in my step daughter drawer. I put them on and grabbed a second pair I found in the drawer that were mine.. the second pair were a pair of very expensive jeans. I thought she might have just put them in there by mistake or just to put them away so they weren't left out.. but no. She walked out of the bathroom and started saying they were her jeans and I told her no, these are mine.At this point I feel like two 14 year olds going back and forth. She was genuinely getting upset, as was I (because they were actually my jeans)... so her attitude and being rude about it made me more angry. I told her what does it matter? We are family, the clothes aren't going aanywhere.. also, I Ilet her wear my stuff and she's destroyed it and I let it go. Now I don't let her wear my clothes because of that.. but she said no it's fine I'll just accept it. By the way, she said her grandma got her the jeans. I said your grandma bought you $100 jeans, she said yes. I know that is a lie.How do I handle this in a mature manner? She is genuinely upset and it's making me feel bad for being upset with her but she is stealing my stuff??? I'm just confused and don't know how to deal with something so silly.Also I forgot to add we have had issues like this in the past.. except with my undergarments.. via /r/Parenting http://bit.ly/2V74w1u