I honestly don't know, as none of my mares have ever done that. It does not look normal to me, however. My advice would be to call your vet. That looks weird enough that if she were mine, I would be taking her to the vet really quick. Other than that, can't really tell you anything. I've never seen that before. She does not look like she's ready to foal, though. No big bag, her vulva appears very tight, and her belly doesn't look as big as my mares do when they foal. Sorry I couldn't be of more help!