I say let her wear the suit. You already made the decision when you let her go into the boys' department and choose it. To not let her wear it would undermine her confidence in your support. If there is flack, which I highly doubt, then you can let her know that you believe in her and think she looks very cute in the outfit she picked out.

Now for a slight hijack of the thread.

Quote Originally Posted by Duck on Wheels View Post
A friend of mine, when preparing for her dissertation defense, was instructed to wear "a tuxedo or the equivalent" (unisex instructions based on decades of almost only men taking PhDs). She went with the tux, a tight-waisted one that fit her figure... .
Where did your friend defend her thesis? When my husband went to his thesis defense (U. of Wis-Madison) he did wear a tie, but no coat. In fact, none of the profs wore jackets. Was that just because it was the late 60's, or a funky department (zoology), or a Land Grant school?