Scaly Leg

I became aware of a scaly leg condition on my Cuckoo Maran at the weekend.  In line with suggestions I found on the forum, I have liberally applied Vaseline to her legs and feet this morning.  There were no crusts on her legs, but the scales were raised significantly.  We only had the chickens in early March and the coop was brand new.  I remove the perches daily and sweep the crevices and perches themselves.  They are bedded on dust-extracted wood shavings which are raked over daily and all poo removed.  The shavings are replaced completely every few days.  They don't have straw at the moment because they throw it out of the coop! 
Some questions for you experts out there - firstly, how often should I re-apply the vaseline on her feet and legs before I can assume I have suffocated the mites?  Should I be using anything else on her legs as well?  Can I assume at the moment that the coop is clean?  I have checked the other five chickens who all have beautifully smooth legs.  Many thanks in anticipation