Did the vet explain to you what it is? Sometimes bulldogs get hot spots... it's a small area that breaks out and becomes moist, then it dries up and becomes a scab. They can be hard to see cos they're under the fur but you'll feel them when you stroke over the area. Is it kind of like that?
It can be food related and if it gets out of hand it can develop into dermatitis. You could maybe try to add some coconut oil and/or greek yogurt to her food and see if it gets better from that.
What food is she on now?