I emailed her back earlier with this:
"It is hard to see but, It looks like a prolapsed pouch. That's just where part of the lining of the pouch is sticking out. Sometimes that happens if she was grooming the area. You also sometimes see that when they're nursing and after the joey is out of pouch. It usually goes back in on its own. I will post it and see what others think."
Then I sent a follow up email saying that if there's odor, discharge or discoloration, that could be something else entirely.