How do you write a letter of recommendation for someone who got an A in your class, but who you've never talked to outside of class?

I taught a large class last summer, and one of my students asked me to write a letter of recommendation. I said yes, and at this point I think it is too late in the application process to change my mind.

The student got an A in the class, but never came to my office hours or talked to me at all before she asked me for a letter of recommendation. She also hasn't done anything specific to distinguish herself. At this point I'm really not sure what to write about her, although she did give me a "brag sheet" with information about her interests and previous projects.

How should I go about writing the letter?