The best way for Diane to deal with this setback is:
a. She should find a native Chinese speaker to tutor her or possibly even be her roommate.
This option allows Diane to continue to immerse herself in the language and culture, which is crucial for developing fluency. Engaging with a native speaker provides her with the opportunity to practice conversational skills, gain insights into the language nuances, and maintain her motivation to learn Chinese. While continuing her classes and reading news sites is also beneficial, personal interaction with a native speaker can greatly enhance her language skills.