I always try to appear before her in "business casual" attire, but we're in Seattle-ish, so business casual can be jeans and a nice top. I never dip below that for my sessions. Even if I was going somewhere afterward, I wouldn't wear just a t-shirt and sweatshirt or anything. I view sessions as a business transaction, so if I wouldn't wear the clothes to meet with my customers, I wouldn't wear the clothes to meet with T.

This rule is easy for me though because I live 5 minutes from her office. If it was out of my way, I would probably relax my rule.