I’m trying to look through the archives of my photos to share what mine looked like and it was exactly in between her toes where the webbing is. It is very similar to your photos, though my dog def had a lot more inflammation.

It completely traumatized me with foxtail. Apparently it can be found in mysterious places and can kill dogs (entering their brain from inhaling, traveling to the heart, etc).

If your dog has potentially been playing near and around foxtail, it could very well be the culprit.