Answer:
The adjective clause is: "which she considered the most beautiful dress ever made".
The word modified is "dress".
Step-by-step explanation:
A dependent adjective clause can be defined as a group of words containing a subject and a verb. Its purpose is to modify a noun or a pronoun by providing further description or information it - similar to what an adjective does. Adjective clauses are often introduced by relative pronouns such as who, which, or that. They are dependent because, without the main clause, they'd make no sense.
In the sentence "Amanda bought a prom dress which she considered the most beautiful dress ever made", the adjective clause is "which she considered the most beautiful dress ever made". It is introduced by the relative pronoun "which" and its purpose is to modify the noun "dress". Therefore, it is not any dress. This dress is the most beautiful dress ever made, in Amanda's opinion.