Yep, the vet said that her first heat probably triggered it. Had to have her fixed right away so she would not go into heat again. Just did a quick Google search to make sure I was not giving you bad info and found this...
DEMODECTIC MANGE
"We typically see demodicosis occur in dogs entering puberty, although some puppies will display signs earlier. For females, the first heat cycle may trigger symptoms and even though we may be able to control the symptoms, each time the dog goes into heat, they may recur."