Scab on golden retrievers chest

Question
I was brushing my 1-year old golden retriever tonight (something I don't do as much as I should), and I apparently pulled off a scab with the brush -- suddenly there was a red, raw, slightly bloody patch the size and shape of a quarter on her chest.  She had a very, very small patch of demodactic mange on her face about 6-months ago that healed with a little ointment.  Another possible cause -- I discovered while cleaning the wound (tonight) that she has FLEAS!  I was really shocked, since she's on Revolution and I've never seen even one on her before (and I'm pretty good at finding them) -- I managed to find about 10, so she has a pretty significant number, I'm sure.  First, what should I do about the wound, and second, why would she have fleas while on the Revolution?  It's about another week until she's due for her next treatment.

Answer
Golodens are prone to skin infections.  I fshe had mange and you only spot treated her, then it could be an area of active mange mites.  REvolution is not a good flea killer.  It is slow, so the fleas in the environment can get on the dog and live for a long time before the Revolution finally kills them.