D1 refused to attend any class. Not her style. (Confidence, not laziness or disinterest.) But she did meet with a friend of a friend who taught in the dept my kiddo wanted. She could reference that in her Why Us. (And she did later study with that person.)
You really don’t “need” to sit in or even contact a prof. You DO need to know what the college wants. You do need to show, in the Why Us, that you are interested enough to have the details straight on this college, why you match them. That’s the critical part of “interest.” That you “get it.” Not that you flew or drove into town, sat in on a class. Any number of kids can go through those motions and still not “get” the college.
Where it can help merit is if she does match what the college looks for (including institutional needs) and they really really want HER. That starts with her own homework on the college, her own self match.