I'm confused

So I'm really confused on why my mom is always questioning me or getting mad at me for locking my door. She knows that my sister is so extra and bothers me 24/7, yet she always asks why I locked my door. She always says that my sister won't bother me, but we both know for a FACT that she will barge right into my room, hug me and not let me go, even when I ask to. Now that might sound sweet, but my sister literally hates me. She doesn't love me in any way, and even told me that I ruined her life and that I should die (two separate occurrences btw). My sister knows I HATE when she touches me in any way, so she does it to bother me on purpose. She even says it herself. "I haven't bothered you in a while."
I just really wanna know someone else's opinion on this and I just didn't know where else to go....