So i trusted my sis with my diary, and she broke my trust?

I have two sista's and the youngest will take anything that she can get her hands on because she doesn't know betta yet.My other sister and I found a cabinet she can't go into because even if she put's a chair there she can't reach all the way to the top, and we both hid our diaries on the top shelf in there(P.s she started writing a diary because i did)and for about six month's it was all good we both promised to never read eachother's diaries, and i completely trusted her to keep her promise beacuse i kept mine.Just a few days ago i walked into the room and she was on the Comp, and her HW folder was open and there was pages ripped from her diary on it, and as i took a look at it i saw some of the poems i wrote in my Diary in her folder, how likely is it that she wrote the exact same poems that i did? So when i asked her she picked up her folder and closed, making me positive that they were my poems, so i asked her to hand them over, and she said that they were her's.So we started to argue and that's when my mom came in, and i told her to just tell my sis to give me back my poems, so she was like i didn't take it but i'll rip these up in front of you, so she began to rip em and i grabbed them from her, she began to cry and she locked herself in the washroom so later on when my mom asked her if she copied them from my diary she said yes.I am still really mad but it's kinda hard cause i live with her, and how do i know that she only copied my poems, and that she didn't read my diary.when i ask her why she did she get's really pissed of and leaves without saying a word.Sometimes i really have to write in my Diary, so i can't just not write in it, and i can't risk leaving it in my locker at school, and i can't trust her anymore so i don't know were to put it,she'll probably find it when i'm not hme and read it again.UUUUUUUUUUURRRRRRRRRRRGGGGGGGGGGGG… i just don't know what to do anymore.