I'm starting  to think SD15 a compulsive liar. I'm currently disengaging from her but DH is also at his wit's end. SD15 will lie about literally anything, even things that there are no reasons to lie about. For example, one of her chores is to load and start the dishwasher. SD10 asked if she could unload the dishwasher and we told her go for it. Instead of telling us that the dishes in the full dishwasher were dirty and that she forgot to start it, SD15 tells SD10 to stop unloading, making it look like SD10 abandoned her job. She then sits back and watches as we lecture SD10 on finishing what you start. SD10 is afraid to tell on her sister so she says nothing. I then discover that the dishes are dirty, the dishwasher is full and SD15 is at fault. DH asks her why she didn't start it or say anything to us when we were talking to SD10. She says, "I didn't forget, I just didn't start it because it wasn't full enough yet and I told SD10 to stop unloading it because it was full of dirty dishes." So she basically says in the same breath that it was too empty to start but that it was full of dirty dishes. DH then brings her to the dishwasher and asks if it looks full or empty to her. She just shrugs. She is now grounded again and currently deep cleaning the entire house.

The thing is, this is a weekly if not daily occurrence with SD15. She does or doesn't do something, we ask her about it, she lies, we know she's lying because she isn't very bright, and then she loses privileges and has to do more chores. Why doesn't she learn? What else can be done to get her to understand? The rule in our house has always been that you will get in far less trouble (or not in trouble at all) if you own up to your mistakes and work to correct them or better yourself. But she never does. She either lies or lets her sister take the blame. 

SD15 also steals random things from me that at one point I wouldn't have had an issue with letting her borrow (necklaces, clothes etc) and keeps them in her room. When confronted, she claims she was planning on returning it, even though she's put it in her drawer or jewelry box or hidden it. Each time she does this she's loses privileges and gets grounded. She still continues to do it, and does the same thing with sweets/snacks-- instead of asking if she can have something or just eating her share and saving some for everyone else, she takes things and hides them or lies about taking them. Her dad and sister have special dietary needs and therefore have certain foods that we buy specifically for them. Instead of consuming the "regular" version of these foods she will take theirs, eat the entire thing or just leave a basically empty container, and not say anything about needing to replace it, so when SD10 or DH needs it, it isn't there. She will then deny eating any of it, but we know it's her because we've found the wrappers in her room.

Please share any advice or things that have worked for you.