It doesn’t matter that she knows about shaving during nine days. It is a matter of first impressions. As you can see from the OP, girls know about the problem of shaving and yet still have an issue with it. First impressions are very important when it comes to dating. You can make all kinds of excuses that she should be able to tolerate the beard, she should be able to imagine what you look like without it, but lemayseh, the way she sees you the first time does make a big difference, and therefore many Rabbonim will matter shaving for a date.
