The correct option is C what she thought to be her meal - object of a preposition
A noun clause is a dependent clause that functions as a noun. It usually
begins with what, whatever, whom, that and other such relative
pronouns. A noun clause can act as a subject, object, predicate
nominative or object of a preposition, in a sentence.
A noun, noun
phrase or a noun clause that comes after a preposition (to, for, with,
etc.) is called an object of that preposition.
Option C is correct
because "what she thought to be her meal" is a noun clause, where "what" is a relative
pronoun, "she" is the subject and "thought" is the verb. This clause is the
object of the preposition "of".
Option A is incorrect because "With the leftovers of" is not a clause, but a phrase.
Similarly, option B is incorrect because "what she thought" is a phrase, it is a part of the noun clause, not the noun clause itself.
Option D is incorrect because "she scurried away" is the main clause here, it isn't a noun clause as it does not function as a noun.