Which words in the sentence are the complete noun clause?
whatever your friend did was her own choice, matthew.
a. her own choice
b. matthew
c. your friend did
d. whatever your friend did

From the choices given, the complete noun clause in the sentence is:

D.whatever your friend did

Noun clause begins with words such as whatever, whenever, and the like. It is a dependent clause which functions as a noun, subject, direct or indirect objects, predicate nominatives, and preposition object.

I’d go with letter d