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Did they come up suddenly?
Is she an indoor or outdoor dog?
What is her weight?
Is there any hair loss?
Is the skin itchy at all?
Is there any scale or flaky skin?
Mange mites usually cause hair loss and bald spots and this isn't the typical distribution on the body where we see mange, so I don't think it is mange.
It sounds more like a hypersensitivity reaction which is pretty common and sounds like your description. It can be due to something like flea bites or just about anything they have been in contact with. You can treat this with an antihistamine and some cortisone cream on the area.
Let me know her weight and I can give you a dose of benadryl to try for a couple days.
You can give her 12.5 mg of benadryl every 8 hours. Try this for two days and see if that takes care of it. You can buy the cortisone cream at any pharmacy, used for humans (is the same as for dogs). Buy the strongest one and rub it in the area. She may lick there and it won't hurt anything, but try to let it absorb well first.
If the rash isn't better in two days, I would see your vet to make sure something else isn't going on, or she may need a stronger steroid medication to clear it up.
To verify, you don't think it is a parasite? I have another rescue dog and three cats and I certainly don't need this little girl passing anything on to them.
I can't be sure by any means, without examining in person, so it is difficult to say with certainty. But usually, a rash as you describe in that area is not a parasite.
Mange mites usually show up with bigger sores, bald spots and hair loss, and are more common around the face, ears and top of the body more so than underneath.
Again, I can't promise that it isn't a parasite, but from what you describe it sounds like a hypersensitivity reaction.
To be safe, you could keep her separate for a couple days to see if it clears up.