As mentioned in today's review, there was only one variant cover that showed the Last Daughter of Krypton as a zombie:
That is an homage to a piece of art that began as an Adam Hughes pinup and was later used as the variant cover for Supergirl and the Legion of Super-Heroes #23. And the marks on her face seem to line up with the ones on the toy, too!
She did appear on a second cover, though there she was her normal self:
That is clearly an homage to the iconic Crisis on Infinite Earths #7, but it also began as something else. The art is by Arthur Suydam, known for all those Marvel Zombies covers (and for being a nightmare to exhibit next to at a convention); after so much Marvel, he decided to do a DC piece for fun, and opted for one of the most character-packed covers in history. He sold it as prints himself, but now DC has printed it on an actual product... almost.
If you look at the original art, Supergirl was being offered up as the feast for all these zombies: she's still alive, and awake, and has an apple in her mouth like a roast pig. But on the newer cover, she's at least unconscious, and there's no more apple. The new painting of her has simply been laid over the old one (the spot of skin on Superman's right knee even used to be part of Supergirl's wrist), with everything from the S-shield down being identical and the new body twisted more toward the front - which means that instead of coming off her shoulders, her cape now seems to fall out of the back of her head. Whoops!