What can I do for my dog's rash?

[Suzinka]

My dog was out in the woods.  We don't see any ticks on her (but they are in those woods) and we don't see any bite marks.  She has a big, round red rash on her underside in the crease of her rear leg, and it feels very hot.

[ginger899]

To cause an issue, a Tick would have had to be embedded and feeding....and you didn't find any, so you say.

So my next thought is a sting? A bee, wasp or hornet might have stung her. Red ants might have bitten her.

Anothttp://www.medhelp.org/posts/Dogs/my-dog-high-liver-enzymes-and-increased-thirst-urination--but-its-not-Cushings/show/2995710her thought -she might have come in contact with an irritant plant. Even stinging nettles can cause a horrible red rash on a dog's belly or inner thighs. Depends where you live. Is there any poison ivy? That's nasty.
In the UK apart from nettles we get Hogweed too, which can cause skin irritation.
There are many other plants which could cause a rash.
How is she otherwise? Healthy and normal?

Bathing the area with cool water might help. Benadryl cream is great for stuff like this, but she will probably lick it off. An dit has other things in it like zinc oxide, etc which might not be great for her to lick!
It might die down on its own and if you can soothe it that will feel nice for her.
I'd say try just cool compresses. And if she is no better in say -a couple of days, or if she shows ANY other symptoms, even more tiredness, appetite loss etc take her straight away to be checked by a vet.