Agree with female Redhead here. As was stated above that white mark, the facial marking is fine for female Redhead.... Remembering that there can be variation between individual birds.
@ egosnell2002... In my experience, Redheads usually mix in with Scaup, but I have seen plenty of times where all 3 species (Redheads, Ring-neckeds and Scaup) are on the same small body of water.
@ Millipede...as with many species, the more you see this species(even females), it will become easier to differentiate them. I always recommend using a field guide with true pics as well as one with drawings, as both have pros and cons, but used together can often give a clearer understanding of field marks, plumages, etc.