I HAVE AN IMPORTANT FAMILY QUESTION...so last week me and my younger sister got into a small argument but?

it ended up becoming a bigger issue than it needs to be...so last week I used her car (my car was in the shop) to run very important errands regarding my case (I'm suing someone) and I also went grocery and gift shopping...so as I was carrying all my bags into the house, I happened to have left some important doents in her car...soon as I got home she left. When she came back I asked her about my folder with all my evidence regarding my case...she told me she threw it away! I was so upset I almost had a panic attack but she didn't seem to care! She told me it was my fault for not bringing the papers inside the house and she thought it was trash...I was too upset to argue with her and I went down to the underground garage to the dumpster and search for my folder. I couldn't find it and she didn't offer to go look until my mother told her to. Literally 30 seconds later she found it...after that she cussed @ me saying F-you and other things I don't wanna say :( So since last week she hasn't spoken to me. And I soon got over it...but what made me go off is when I came home with food for myself, my boyfriend, my son and my mother and she had the nerve to make herself a plate! I was so mad I told her she has her nerve and to get her own food...my mom yelled at me and said I was wrong, I let it go. So to release my frustration I vented on my facebook page on how I have to let go of ppl in my life sometimes including family member in order to achieve my life of peace...I guess she saw it, told my mom and my mom cussed me out. Idk what to do...I felt like my sis should have talked to me about it instead of getting my mom involved...am I wrong or am I fighting a losing battle??? SORRY SO LONG!