Is this rain scald?

I have recently noticed that my horse has bumps along her back under her coat. At first I thought this was a major case of dirt due to her paddock being quite muddy and her rolling. Although now after reading some other posts on the subject, I am convinced it is rain scald.
I don't have a photo - But basically they're hard-ish bumps/scab looking things, deep into her winter coat. I had originally tried brushing it out, but as soon as I realized brushing didn't help much I gave her a proper wash, and noticed it loosened it a little bit and some came out, but she still has quite a bit there.
Is this rain scald, or something else? And what kind of treatment can I use on her to get rid of it?

Too much typing ......to explain it all, but in a nutshell the characteristic symptoms of rain scald give the impression that large droplets of water have scalded the skin. Check for affected areas of skin over the rump, loins, saddle area, lower limbs and along the lines of natural water drainage over the skin. Problems start with the skin exuding a sticky secretion, scabs will form and when you remove them you see areas of pink, moist skin that sometimes bleed a little.
Samples can/should be taken to prevent confusion with ringworm (esp. In the early stages) or seborrhoea (excess grease production).

Affected horses should be kept dry and exposure to wet weather and muddy conditions cut to a minimum.

Skin samples can be examined microscopically for the bacteria to confirm the diagnosis.

I don't think your horse has rain scald, but what is called simply a Skin Fungus. It is very common and nothing to fear as it is not a contagious condition to humans. In order for the condition to clear up the scabs need to be removed with vigorous brushing with a stiff brush. My Vet mixes up a concoction I think that only he knows the "recipe". Bathing the horse with an Iodine based shampoo will help, but removing the scabby bumps is necessary.

With Rain Scald usually fairly large patches of hair come off and the skin is very pink and sometimes bloody looking. I've seen Ringworm that usually manifests on the muzzle and under the belly without hair loss.

Thanks for your reply, it's made me feel quite a bit happier! Honestly I don't know a whole lot about infections and treating them so I was a bit worried when I read about rain scald and realized I should have been bleaching her brushes/saddle cloth/various other objects it has touched to even make a slight improvement. I will try bathing her with iodine and trying to remove her scabs as best I can.
Also, with her condition, do you think clipping her will only make this worse? I was planning on clipping her, until I noticed the small scabs on her back. I wouldn't want to do any thing that will make things worse/uncomfortable for her.

I've never clipped a horse's coat, but have treated many with the skin condtition I described. So I think I'd recommend not clipping your horse until the skin condition clears up. The bumps are not especially painful, but are tender so clipping might be more so uncomfortable for your horse. Not only that, but the scabs/bumps need to be removed from the skin's surface for them to heal. If you need more info please PM me...

So turns out she does have rain scald, it's quite nasty too. She's currently being washed in Betadine once a day, and that seems to be making an amazing difference even after a few days of treating it. Thanks to everyone for your suggestions!