My sister keeps stealing from me

Posting for a friend who needs creative solutions that lead to permanent change and won’t damage her relationship with her parents. She’s in the process of getting a lockbox but she ultimately feels violated and wants to be able to feel secure with her personal belongings in her home.

my (22f) sister (24f) has been stealing from me and i found out she stole my ear plugs that are made out of crystals, she doesn’t even have stretched ears. at least not stretched enough to steal my 00g plugs. on top of the fact that she’s stolen other pieces of my jewelry, my clothes, and other important stuff.

yesterday i went in her room and just found so much stuff i thought was missing or i thought i lost it only for it to be hidden in her things bc she knew she’s wrong for stealing my things. it’s been an ongoing issue for YEARS and nothing i do seems to make her sit and realize she’s so wrong for thieving off of family, not even telling my mother bc she takes her side. so ima have to take matters into my own hands bc obviously nothing else has worked

i’m just so over it like i shouldn’t have to deal with this especially bc when i came back i told myself i was gonna try to keep the peace and ease into rebuilding a relationship and making things better only for her to still be such a piece of shit behind my back and even to my face at times. it’s genuinely the worst feeling in the world to have to constantly be let down after being the only one to make an effort, so instead i’m just going to either confront her and my mother with everything i’ve found of mine in her room or i’m going to end up going crazy on her and then moving tf out and never speaking to anyone except for my brother again

i’ve been dealing with this for over 4 years now i genuinely am losing my mind, i’ve lost ab 2,000$+ from her stealing from me, and my mom just allows it and even enables it. so ima do everything in my power to stay true to myself but im so tired

thing is, i don’t have a room. i sleep on the couch. everything i deem extremely important is right next to where i sleep bc im a very light sleeper and will wake up if i hear rummaging. everything else is in two closets next to her room and the bathroom. if i take drastic measures my mom will be on my ass. if i do nothing i will end up with nothing. so i’m in a rock and a hard place type of situation. when i moved out she took our shared room, tried selling or donating or throwing/giving away the things i left behind, and basically forced me out of my room with my bed and everything whenever id come to visit after moving out. but now that ive been staying here for a bit, shes gotten brave enough to think i won’t notice what things are missing