Is she spayed? Once a dog has gone into heat, she can't have an inverted vulva anymore. If she was spayed young, that could be the problem, but I think the issue would have been dealt with by now. If she's not spayed, she might be going into heat. Keep her away from unneutered males.
But that does look fairly icky. Better have a vet take a look.
But that does look fairly icky. Better have a vet take a look.