Hi K.!
First of all....all of us women have been 14 and 15 years old before, and KNOW how difficult that age can be for anyone! No Matter how great our parents were, it was still difficult to be 15!
But you are being "double-whammy'd" with this age AND a part-timer in your house. Of course she is old enough to know better, but that certainly isn't going to stop certain behaviors, because when you're 15 every action is based on emotions, and "common sense" has temporarily moved out of your brain!
Sure your stepdaughter is jealous, and you've already been told that fact by her own mother. I'm sure it's not an emotion that you were intentionally trying to bring out of her. She's jealous because she thinks YOUR kids have something more than she does. She's feeling like THEY are more important than HER.
If it were my situation (and it was), This is what I would do again....after I found the stolen items like you did, I would actually take them out and hide them from HER. Then, I would invite her to a 1-on-1 shopping trip with me to buy the items she stole from my daughter. DON'T tell her that you "know" about her taking the other items. Just find a way to strike up a conversation about wanting to take her to Walmart (or whereever). I would tell her that "it's been a long time since we've done something like this together, and you probably need some new makeup and stuff. I have $20, let's go get some new colors for you"...try to find the things she stole, and say "oh about this this"....etc...again..never tell her that you know, just let her "honest heart" go through the guilty process.
Then, after she's left your house, and gone back to her mom's, put the make up BACK in your daughter's drawer, as if nothing happened in the first place.
I've had a stepdaughter for 13 years, and have had similar problems. I'll be honest, I felt very "wicked" in a sense, but I never told her that I knew she was stealing. Even to this day I've never told her and she's 22. She'll figure everything out for herself one day. I did it to protect the kids from "eachother". Even though my stepdaughter THOUGHT she was stealing, my child never knew. After I spent a little "quality time" with my stepdaughter, and bought her things she THOUGHT she needed, the stealing stoppped.
All she really needed was to feel just as IMPORTANT as my other kids that her dad and I shared. So, once I focused on that issue, rather than the stealing, it worked itself out.
Being a stepmom is so hard each and everyday. There really should be a "college course" now-a-days about blending families!!!
She's only a part-time visitor in your house right now, which makes her feel LESS important than she actually is to you. She's not mature enough to simply understand that you love her because she's your husband's daughter. When she visits, you need to find something SHE'S proud of to bring out in conversation around your kids to sort of "show her off" every now and then. By doing this, you will begin to emotionally connect with her, and she will begin to "loosen up" in your home, and not feel so "less than" because YOU are making her feel important.
You never know, it could turn out like my situation. Today, my stepdaughter confides in me with her "serious matters". I'm like her "practice parent". She will come to me with ANYTHING and ask me for advice, first. I created a "connection" between us when she was younger, and that created a bigger bond of trust than I never expected.
All I wanted to do was to make her more self-confident and loved in our home, without effecting the other kids. It takes a LONG TIME to get through this, maybe up to a year, but the results can be everlasting.....
Good Luck K.. I'll be thinking of you.
:o) N.