I'm iffy on it. It's got a hook, but it feels incomplete. I see the main character (young girl) and I see the inciting incident (finds a monster in the closet). But what I don't see is a goal or need, and it's blurry what the stakes may be.
Also -- and this is just my own personal quirk so do with it what you will -- I'm not a fan of log lines presented as questions. At best they feel evasive; at worst, condescending. The reader doesn't need you to ask their question for them.
A log line's purpose is to intrigue. I'm not so much intrigued by this as mildly flummoxed. Give me more to go on.
My two cents.