Surprised involves other muscles moving too. Her mouth doesn't frown, her cheekbone doesn't move and her cheek doesn't expand. She's just frowning, Jack Hughman's Wolverine style - where he'd only frowns and changes nothing else on his face. (Dude doesn't even squint, it's a fun build up.)
The reason it looks weird is the jump, it's not a smooth transition. The colour in her eyes, as well as the eyelids, change immediately - which is pretty weird, but it probably won't look that way when you don't have time to stop and analyze it frame by frame.
Human emotions have build ups, they aren't easy to promote in three-frames.