Comic books are worthwile to read by everyone because they are another art form. Whether a book has photos, small print, boxes, whatever, they all have a meaning. The stereotype that comics book are just for kids or are only superhero related is outdated and leaves the wonderful world seeming closed off to so many.
Hey there! I believe your answer is Her wanting to buy a Christmas present for Jim. I know this because in the story, Jim sells his favorite watch to buy Della's favorite combs, and then she feels as though she owes him for that. So, by selling her hair, she can use the money to buy Jim a gift just as good as the one he got for her. I hope this helped!
Thanks, have a nice day!
~Steve
The type of figurative language is an idiom.