Claire is much than her sister Charlotte. (clever)

Claire is much more clever/ cleverer than her sister Charlotte.

Explanation:

The comparative form of the verb is the use of comparison in a verb. And in the case of the word "clever", there are two ways of comparison- more clever and cleverer.

Now, in the given sentence "Claire is much than her sister Charlotte." The comparative "much" is already used in the sentence so we can either add "more clever" or just simply "cleverer" to add/ emphasize Claire.

So, the final sentence will be "Claire is much cleverer/  more clever than her sister Charlotte." Either way, the use of both is correct.

did you ever get an answer? i'm on the same question : (