Chas ~ Demodectic is a thousand times better then Sarcoptic! (Well none would be the best!)
As I mentioned .. most humans and dogs carry the Demo mite on their skin with no problem. It's when the immune system gets run down it rears it's ugly head. The mites actually suppress the immune system which is why they take a hold which is why the good diet ie with no grains is good.
Also might be worth putting her on some vitamin supplements to get the immune system up.
How old is she? Puppy's immune systems don't come in to their own till about a year... so it is possible for a relapse up until then.
You're quite right about the stress of a kennel bringing it out. Please please do not let your vet convince you it is not treatable. It totally is. It makes me so mad when vets say that.
Is she spayed? Coming in to heat can irritate the mange in to activity.
Trisha ~ I love Greyhounds. They are so cute when they are born, look like big fat lab puppy's lol.
I used to have a big 38 Kilo blue brindle male.
And you're quite right, they are the laziest dogs ever! Big myth they need 30 mile walks each day