That fight is right after the entrance into the Blackpits area. It is some ways from the doctor's cabin.
Strange bug, but then, as far as the fight with Natalie is concerned, just lowering her HP isn't enough. There's an extra step you have to do.
you have to knock her down. Just knock her down early on and damage her until the fight stops.
Although with this bug, I'm not sure the fight would actually stop like normal.
