Was she actually diagnosed w/mange or speculated - you said no hair loss, was this found on a skin scrape or just observation on vets part?
May be heading into hairloss stage.
She's 4.5 months, I am guessing she had a recent rabies shot? was this with other vaccines at the time or within a couple weeks to a month.
Note: THIS is NOT an anti-vaccine blurb, simply to explain how/why mange may have come to fruition.
First, her immune system hasn't fully developed - it is estimated approx. 6 months. When a vaccine is given, it supresses the immune system defences that deal with other pathogens as it works to deal w/invading vaccine virus or bacteria, a weak or underdeveloped I.S. may not be able to manage, so demodex mange - which is already present and normal under most circumstances proliferate because of immuno suppression.
The immune system once it has dealt w/rabies and/or other, may restore (with good nutrition) on it's own and fix the problem.
A little immune support would help too. Vit C if you want to keep it simple, an anti itch bath with a neem shampoo (formulated for dogs) as mentioned by Ruth.
I would wait to spay too...should never have surgery within months of a vaccine or pesticide treatment to be on the safe side and once the immune system is in top form - the adrenal glands are responible for sex hormones and are part of the endocrine (immune) system, as well the pancreas all work in tandom, so it is important to make sure you are comfortable with surgery and there are NO issues concurrent at time of spay - meds, prevention, vaccines, itchy skin, diarrhea.
here is a link from a company I have used products and was recommended by my Vet...it is animal specific and can dose easily by weight (instead of human product) in her food
Omega Alpha Pharmaceuticals - HealthyPet