Hi, to me it looks like an allergic reaction to something, either environmental like new shampoo, laundry soap, or a new household cleaner or a bug bite of some sort like ants or fleas. I would give her a bath with a gentle soothing shampoo, rinse her well, you can even use some warm water and plain white vinegar as a final rinse, and give her a Benadryl, I give my guys weigh 45 lbs and get 1 Benadryl. If this doesn't help and you don't see any improvements, then take her to the vet to have it checked. Yeast infections usually look more yellowish and have a smell or odor to it. I don't have any experience with yeast infections, but have heard it smells like Fritos. I do have experience with allergies and rashes as both my guys have allergies. I hope it clears up and she feels better soon. Is she itchy?
This is what a yeast infection looks like.