am i overreacting???

i currently share a room with my younger sister. we moved houses to live with my 86 year old grandad last year, we never shared a room up until then.

our room is a big room though, big enough for two double beds and plenty of furniture - we both have a wardrobe and a chest of drawers each, so we have enough room for our clothes etc, and they’re kept separate.

i’m a size 4-6, she’s a size 10-12. i also love make up. i have so many lipsticks and palettes etc. that aren’t cheap! £20+ per lipstick, and £40+ palettes etc!

she’s always been murder for taking my things but since moving in, it’s gotten so much worse.

she’s wearing my underwear, my clothes, my make up, my shoes. everything she can get a hold of. my sister isn’t tidy whatsoever. she doesn’t even wash her clothes, they just end up thrown all over her floor. my make up keeps going missing, she’s taken over £200+ worth of lipsticks, all i work hard to pay for!!

not only that, because of the size difference, all my clothes and underwear is stretched and mostly all now too big for me - meaning i have to buy more.

i bought a crop top a few weeks ago, that i was saving for my holiday with my boyfriend in a few weeks. she went to comic con, took it without my permission and drawn all over it to suit her cosplay.

but she lies about everything!! she’ll tell me she can’t fit into my clothes and acts as if i’m being stupid just for asking her.... then she’ll come downstairs wearing it. i’m honestly at my wits end. all of my clothes are going missing, virtually most of my belongings. i feel like i’m spending all of my time screaming at her, and we just aren’t close anymore because of it. but it’s getting me down majorly and i genuinely feel like i can’t live like this anymore 😭

(i’m trying to save up to move out, but i plan to go to university next year and the student finance system is a joke🙁)

Advice please??