Just found a rash on the inside of my dog's hind leg?

She's a Shih Tzu/Maltese/Chihuahua mix, about 4 years old, in case you need to know. Just now, my sister pointed out a bright red rash that seems to be in the crook between her inner thigh and her belly on one of her hind legs. I didn't touch it of course, she was upset that we were prying her leg away from her body, but it looked like it could be bites of some kind, but it could easily be irritated by being rubbed or something. It's hard to tell the source, to be honest.

I'm wondering if any human rash treatment products are safe on dogs, or if there are any home remedies for this? Of course, it would be ideal to take her to the vet, but because it's expensive, I'd rather see if we can fix it at home first. We have a couple of different all-natural lotions and creams in the house, and on a person I would usually use Desatin cream, but I'm not going to put anything on her body before I know it's safe for dogs!

Can you tell me if any of those things are safe, or if you know of any other home remedies for a small rash?

Thank you!