Sore on dogs mouth

[bluebird3]

Does anyone know what this is? I've just found it. The bottom bit is a black scab. On a dog walk this week the group went over a wasp nest and the dog walker thought my girl might have been stung. Is this from that? Should I take her to the vet? It doesn't seem to be sore or bothering her.

Bump

I'd take her to the vets as I worry daily about alabama rot, starts on feet and muzzle

Thanks for the reply. I think I'll ring the vets tomorrow to see what they say. I've remembered that she was running and sort of fell over her feet on the concrete ad may have grazed it then. I'm hoping it's that as it looks more like a scab now.

Does she have plastic bowls? They can irritate.