Lady Blanche's headdress.
Melissa, in the morning, has shorter hair, but by lunchtime her hair has grown quite a lot.
Set in medieval times, a notice board listing planets refers
to Uranus, not discovered until 1781. (Although "Princess Ida" is set in medieval times, this production is set on a Victorian estate as a play within a play, which may account for the apparent anachronism.)
As a previous commenter pointed out, "Princess Ida" is set in
medieval times which makes the several references to various characters smoking cigars somewhat problematic, since tobacco usage didn't become prevalent in Europe until quite a few years after the discovery of America. (Although "Princess Ida" is set in medieval times, this production is set on a Victorian estate as a play within a play, which may account for the apparent anachronism.)