As you say that, apart from her itching, it's not really going anywhere, something you could try while searching for the root cause, is to clean the area fully with salt water, dry it as much as you can, then pat on plenty of baby talk ...the one with the 'J' name is best ...not sure if I can name it on chat :-)

Keep the area clean, dry and talked up as often as you can and what it will do is stop the area from itching.  If it doesn't itch, she won't try to scratch, and if she doesn't scratch, it won't weep and infect.  That should buy you time while you hunt down the root cause.

Believe me, I've used this method on my dog after spending hundreds at the vets without them solving it ...AND IT WORKED!

If it is eczema then she might need antihistamines or a simple cortisone cream (some, you canbuy over the counter) perhaps something you'd use on babies.  Better to keep it from breaking out and getting infected then needing antibiotics.

 Hi,

I have an Irish cob who also has a similar rash.scabs in his groin area. His flairs up when he gets hot and wet. I find that I have to rinse his legs every time I ride and like you I also sometimes apply sudocream. When I got the vet in he looked at it and said he had no idea what is was of what to do, maybe it was an extension of the freather mite??? not very helpful hey!

So far I have found that dermoline is far better than sudocream as it doesn't go all sticky and flacky the next day. Pig oil is also good for it as well as the feather mite.