Yes, there is a ton of information about demodectic mange on the forums. If you do a search, you'll find a great deal of advice and many others' experiences.
You're right that she should be spayed though. The additional stresses of the hormone surges are liable to bring on resurgences of mange at every cycle. One important thing though, is NOT to spay her until you've got the mange under control. As you're aware, this is an immune system problem - and excessive stresses to the immune system of a dog with a weak immune system is what results in mange. Sure, a heat cycle is such a stress. But so is surgery

So don't do it until after the mange is controlled (you've got several months before another heat is due, after all).