Add size in the title and the name and location of the school if they'll fit. Add measurements, at minimum the length from neckline to hem and the width from one armpit seam to the other. Mention specifically that the item is black, because the photos might make it look gray. Your images are good, but I would lead with an image of the entire garment rather than the closeup.
As noted, clothing is a very saturated area. Start the auction bidding at a price you'd be willing to sell for.
Take out all the references to the current owner. Nobody wants to wear a spendthrift old lady's used clothes.
Keep the clothing in your possession after you photograph it. Not only so you can ship promptly, but also because sometimes consignors change their minds and give stuff away even if it's an active listing.
