The sentence "Anne knew that she would face problems with freshman composition, she worked it day and night" is a fused sentence.
A fused sentence is a type of sentence that incorrectly joins two independent clauses (sentences that can stand on their own) with no punctuation or conjunction.
So, In this case, the two independent clauses are "Anne knew that she would face problems with freshman composition" and "she worked it day and night." The correct way to write this sentence is to either separate the two clauses with a comma and a coordinating conjunction or to use a semicolon to join them.
See text below
Anne knew that she would face problems
with freshman composition, she worked it day and night.
Comma splice
Fused sentence
Correct
Fragment