What grammatical structure is the italicized portion of the sentence?

Although her personality had not changed at all, Megan looked quite different.

adverb clause

infinitive phrase

past participial phrase

elliptical clause

adjective clause

If the grammatical structure that is italicized is although her personality had not changed at all, then the correct answer is adverb clause. Adverb clauses function the same way simple adverbs do - they answer the questions such as why, where, when, how, etc.