I'd offer to take her shopping for a few things of her own. Since there's a ten year age difference, she needs to get to know you better and she's probably also jealous of you. No doubt, your parents have spoiled the baby of the family and they didn't teach her "boundaries" about other people's things.
Spend some time with your sister, but have a firm discussion about what's acceptable behavior and what's not. Compliments go a long way -- "Gee, that color really looks good on you" -- type of thing.
you sister is a sociopath- I'm not joking- doing whatever you want to people without fear of consequences and a sense of entitlement-she needs help-
Hi, I think there is more to this than compulsive lying, I think your sister needs some attention, I think this is a cry for help, maybe go out and have coffee together and have a long talk about whats going on in her life, she might need you more than you know. This is a difficult age and something might be going on. The scissors part is what made alarm bells ring for me. Be nice, talk to her.
She doesn't really sound like a compulsive liar, just an ordinary one. She has reacted to your presence by nicking your stuff and doesn't want to admit to it. Who would ? When I was backpacking, I used to put a padlock on my bag to prevent theft. Just do that and ignore her negative crap. Be nice back if she is nice to you and let her `learn all about harmony and maturity from her big sister. If she starts to trust you, she may even tell you where she has been going and what fun stuff she has been up to.
Maybe get a padlock on your door? you hold the key.
It seems like there would be much more to this story than what you have wrote.
But anyways.... just lie more than what she does.
Constantly put her in a position where she will have to tell the truth in order to defend herself from your lies.
Eventually telling the truth might turn into a habit for her. lmao.
It sounds to me that shes jealous. You have returned home and no doubt your folks are giving you some of the attention that normally she had, suddenly shes having to share affection and she doesnt like it. My gf well as of today ex gf is similar, her jealoousy of me has been out hand and she has twisted lie upon lie to get what she wants all out of jealousy. Today Ive snapped and had enough, now shes saying Im a bully and abusive. Some people have to blame someone else for their own shortcomings which is basically what your sister seemt to be doing. Best of luck, just hurry the decorators along :-)