Nope, she's said nothing about looks. All she said was that Astoria was Daphne's sister, a Slytherin and two years below them. She had Draco marry her because she didn't want Pansy having a happy ending (ha ha).
But then JKR doesn't go in for reams of description. We only found out Ron had blue eyes when someone asked her before HBP. Not many of the actors resemble the characters. Film harry has blue eyes, Emma Watson has straight teeth, the twins are tall ... etc etc. I don't picture the actors when I write (except Rupert Grint ... curiously), I just write the ones in my head.