I'm confused - they had a guestlist and everyone else in the class but her was on it, or none of your students were on it and they decided to exclude her personally?
They had a guest list and all my students were on it. This particular student was also on it, along with a note to exclude her specifically from entering the office.
Ah, I read your post as if you guys literally just showed up and expected to get in. Did they know you were all together?
I think you did the right thing by allowing the rest of the class to attend, but I feel terrible for your student, especially given the push for more women in engineering.