Emma Bloom is the epitome of "looks can be deceiving." When we first meet her, she's an angry violent girl, like Katniss Everdeen going through some sort of narcotic withdrawals. She drags Jacob into an alleyway, presses a knife to his throat and says, "I'll water the grass with your blood!" (5.124). What kind of lawn does this girl have? Yikes.
We learn this is mostly a tough façade she puts on, though, as a way to protect herself. Miss Peregrine says Emma "has a certain flair for the dramatic" (6.32). Which begs the question: What's she protecting herself from?
Well, Jacob reminds Emma a lot of her first love, Jacob's grandfather. Yes, you read that right. No, Grandpa wasn't a creeper, but Emma is actually in her eighties. That's another of her looks-can-be-deceiving traits. In Miss Peregrine's time loop, Emma doesn't age, so she looks forever twenty-one (well, more like forever sixteen, but that store doesn't exist… yet).
Emma falls for Jacob, but we're not sure if she's in love with him because of who is he, or because of who he reminds her of. Guess we'll have to read the sequel to find out.