Does this sentence exemplify an adverbial clause?

“Wherever” is a fused relative word (a pronoun) meaning roughly “Any place that”. So Wherever she goes, she leaves an item of luggage behind can be paraphrased as Any place that she goes, she leaves an item of luggage behind, in which Any place that she goes is a noun phrase.

That noun phrase (with its embedded relative clause) functions here as an adjunct (or adverbial) of place. It doesn't modify anything, it's just a supplement providing additional non-essential information, and hence is semantically non-restrictive.

In the example

[Adv [Comp Wherever] she goes,] she leaves an item of luggage behind.

as I've indicated with the brackets, the phrase "wherever she goes" is an adverb that goes with the main clause "she leaves an item of luggage behind", but the word "wherever" is not an adverb. "Wherever" is the complement of the verb "go" -- it is not a modifier (so it is not an adverb).