Most Helpful Guy
Dress up! If she isn't when you go pick her up then you can say (jokingly) "Oh man! I thought we were dressing up you jerk! Now I look try hard. ;p"
If you're lucky she'll jump out and go put on a smoking dress. Added bonus is she'll probably let you in her house which will make bringing you back to her place later in the night not such a big deal (because you've been in there alrady in a non sexual context).
If she doesn't change, then at least YOU'll look super dapper. And you get to banter all night about how she played you into dressing Bond.