No. It is however ungrammatical if you are trying to say "She saw a derby.", however if derby is a name for someone or something unique than it it correct.
Do you work? is a complete sentence; it is not a sentence fragment.
"She wave." is fragment but "She waves" is a sentence.
fragment
A phrase or clause written as a sentence but lacking an element, as a subject or verb, that would enable it to function as an independent sentence in normative written English.
Fragment.
sentence fragment
It is a sentence fragment
is a sentence fragment
Make each fragment into a complete sentence.
"After the storm," is not a complete sentence so it is a fragment.
A sentence is a fragment when you do not have a noun/pronoun and a verb.
A fragment sentence is a partial sentence. It does not have everything it needs to be a full sentence. For example: "The dog" is a fragment.