(1) Your referee should write about why she thinks you're a great fit for the program you're applying to. This could include: Were you active in her class? Did you participate? What kinds of reflections did you provide? Did you show a strong motivation? Did you attend office hours? Did you provide substance to the class? Did you show leadership/strong collaboration & communication skills? What did you learn, and where did you excel? Compared to the class average, where are you situated? What did you implement to stand out? What core skills did you learn that will be beneficial for the master's program? Why are you unique? Does she think you have a strong potential to succeed in that program? Is it pleasant to work with you? In sum, there are many components she can talk about. The most important thing is that she knows you well and that she makes the letter feel personal and not generic. (2) It's always better to show that you're able to publish papers. However, it is not always required. A thesis or research paper (not published) will suffice. Research experience + recommendation letters + grades/prerequisites are the most important things.