It's sometimes by her butt too, but in the mornings it's not there, only later in the day. She is a year old and broody at the moment. She seems fine otherwise.Nope, that's not molting.
It could be dander... but really looks like she got into something.
How old is she? Is she laying? Can you show a full body pic?
It doesn't seem like it's bothering her. She is not scratching the whole time. In the mornings it's not there, only later and the next day it's gone for a day or 2. I dust or spray my 2 silkies every week with lice and mite powder/spray.Looks like poultry lice... but could easily just be debris of some sort