。
She's much smarter than she looks.
Literal
She [topic-は] appearance [more-than-よりも] much-more clever.
より marks the basis of comparison ('compared to X'), and the も piles on emphasis — 'compared to even X.' ずっと then turns the volume knob the other way: 'far / by a long way / much more.' Stacking よりも and ずっと is a common way to make 'much ~er' in spoken Japanese. The pairing of 見かけ ('outward appearance') against 賢い ('clever') is a classic 'don't judge a book by its cover' set-up.