Being deliberately tasked to "cheer up" someone who's husband just died would be a bit much for me, I think. But maybe it's meant to take her mind off things, working on German and such. I know that she and Professor Dolohov are close, so it makes sense that he'd look out for her. And if you learn German thanks to the arrangement, why not?

I'd just rather not think about school while I'm not in it! This is why your marks are better than mine are, no doubt.

Do you know who else will be there tomorrow night?