Final answer:
The sentence provided is correctly punctuated and does not require any changes. The conjunction 'but' is not preceded by a comma as it does not introduce an independent clause.
Step-by-step explanation:
The sentence in question does not require a comma before the conjunction 'but' because what follows is not an independent clause; therefore, the correct version of the sentence is the one that has no changes: "After a few moments, Jessica said that she loved Morrison's novels but had to finish her take-home biology exam, which was due the next day." This sentence is correctly punctuated as is, with the comma after 'exam' correctly setting off the non-restrictive clause that provides additional information about the biology exam.