Pretty sure this was asked before ...
Anyway, it's probably because Kushina was a Jinchuuriki during her pregnancy, which led Kyuubi to transfer some of his characteristics like the fox whiskers to the baby in her womb. Kushina's mother however wasn't a Jinchuuriki and Kushina only became a Jinchuuriki when she was already older (contrarily to Naruto who had been influenced by the bijuu since his conception and became a Jinchuuriki just a few hours or so after he was born) so Kyuubi didn't have any chance to influence her appearance like that