When you think about it, Marianne hasn't just learned this emotional indulgence from literature. She learned it from her mother first, and the romantic literature she reads just reinforces her idea that this is how people are "supposed" to act when they experience strong feelings.

In this passage from the end of chapter 8, it almost sounds like she thinks Elinor has committed a faux pas by NOT making a demonstration of her emotions!

"And Elinor, in quitting Norland and Edward, cried not as I did. Even now her self-command is invariable. When is she dejected or melancholy? When does she try to avoid society, or appear restless and dissatisfied in it?"