Take a look at the sentence again:
Struggling to capture the nude model on paper, Sima whined that she didn't
have the right pencil at the same time, she realized that this complaint
was the same as saying that she couldn't sink a
basketball because she didn't have expensive athletic shoes.
That she couldn't sink a basketball is a subordinate clause. A subordinate clause cannot stand alone as a complete sentence. Because she didn't have expensive athletic shoes is a second subordinate clause. Two subordinate clauses can follow each other without punctuation.
For future reference, you might want to remember that 99 percent of the time because does not require a comma before or after it. Using a comma with because is a common error.
Go back to the sentence to try again.