If it's raw and oozy (hard to tell in pic) it could be an infection (yeast or some other sort) that started in the fold from moisture or a bug bite and she has continued to lick it. If she will let you wash it with a warm wet cloth, dry it and do your best to keep her from licking it. If it doesn't start to dry up and heal on its own she will need to see a vet.
__________________ Gretchen  Jamie  Logan Charlie Miles Elliot Winnie  Misha  Chloe  |