Advice on what these could be?

For context, we live on the east coast. Not really a wooded area but she walks around a wooded pond behind our complex. Geese, ducks etc reside around the pond from time to time. She doesn't really interact with them. But these spots on her belly have begun to arise over the past few weeks. She has a vet appointment coming up but we want to try & mitigate it as much as possible because it's slowly getting worse. & I havent the foggiest idea as to what this could be.

Any & all advice suggestions would be absolutely greatly appreciated.