The way I interpreted it at that time was "can you make (the semester) less depressing," because the sentence came right after I said, "this semester was pretty depressing." I don't think she meant making the depression less depressing. That doesn't make sense to me at all. But "making the semester less depressing" is still pretty weird, and a weird sentence by itself. How can you make the semester less depressing?
As I said, I thought she implied me to do something to combat the depression, since she's normally a pretty intelligent person. I don't think she would make the dumbest comment among the various possible interpretations we are discussing here.
It's the way she said it that made things awkward and showed her ignorance about depression. It is a disease and certain things become more complicated and don't really work in a normal way. The ignorance is not a fault though, I think. The "advice" might be a good one, intellectually, but it's not quite right emotionally. She did tell me "be happy" before, which I was fine with. But this time I didn't even know how to respond. I have not expected someone makes that weird comment. I think I giggled at that time. What does that sentence REALLY mean? I'm still not entirely sure. Maybe it doesn't really mean anything. It's plain awkward.
And now I know that I should stop talking about this matter with her